Both upconverters and dowconverers are contained in the doagrams. The Global Positioning System (GPS) works on the principle that if you know your distance from several locations, then you can calculate your location. The known locations are the 24 satellites located in six orbital planes at an altitude of 20,200Km. These satellites circle the Earth every 12 hours and broadcast a data stream at the primary frequency L1 of 1.575GHz which carries the coarse-acquisition (C/A) encoded signal to the ground. The GPS receiver measures the time of arrival of the C/A code to a fraction of a millisecond, and thus determines the distance to the satellite.
The Core Subsystems include:
· Front End - the GPS L1 signals (Maximum = 24 signals) at 1.575GHz are received at the antenna and amplified by the Low-Noise-Amplifier (LNA). The RF front-end further filters, mixes, and amplifies (AGC) the signal down to the IF frequency where it is digitally sampled by a ADC. '
· Base band Processor/CPU - the ADC samples of GPS C/A code signals are correlated by the DSP and then formulated to make range measurements to the GPS satellites. The DSP is interfaced with a general-purpose CPU, which handles tracking channels and controls user interfaces. TI OMAP integrates both DSP and ARM processor on the same chip.'
· Memory - the processor runs applications stored in memory. The OS is stored in non-volatile memory such as EE/FLASH/ROM. Applications may be loaded in FLASH or DRAM. '
· User Interface - allows user to input/output data from the receiver using input commands via microphone, touch screen, and output MP3 to the earplug.'
· Connectivity - allows the receiver to connect to the USB port.'
· Power Conversion - converts input power (battery or wall plug) to run various functional blocks.
· FROM http:// focus.ti.com/docs/solutions/folders/ by Texas semiconductors instruments.
Monday, December 3, 2007
Saturday, November 24, 2007
7.CLASSES OF RF AMPLIFIERS
RF. AMPLIFIERS.
Classes of amplifiers class A, B, AB, C, D, E and F
Class A
This circuit permits a simultaneous large voltage and current swing at the output of the device.
The circuit will always be on in this kind of amplifier unless some other switching circuit is added. Biasing is at the midway where current swing will be I max/2
Power efficiency is always 50% or less and cannot go beyond that amount.
Temperature is also another concern that the device may not be overheated.
iD = IQ + I peak cos not
vD = Vcc + I PEAK RL cos lot
PRF = I PEAK 2 RL
2
Effi = I PEAK 2 RL and PDISS = Pdc - PRF
2 IQ Vcc
The conductor angle of class A amplifier is 360o or 2 radians.
It is a larger gain compared to the rest of amplifiers
CLASS – B amplifier.
With a conductor angle of 180o or 3.14radians the circuit is independent of drive level.
When Vin exceeds a threshold value (Vo) the output current (Io) = G (Vin – Vo) and when it falls below threshold, Io = O
If G is trasnconductance and Vo is the bias voltage
Vin = Vb + Vicos wt
When the amplifier is on the output current mirrors he peaks of the inoput sinusoidal voltage .
The peak of the sine wave tips of the Io is just the trasconductance times the amount by which the input volatage exceeds the threshold that is
Ip=(Vi – Vx) G
Io(t) =IP/3.14 + IP/2 coswt +2Ip/3Pie cos 2wt – (2Ip/15pie) cos 4w + ----
Pdc = VccIp/pie
PRF = VPEAK IPEAK/2
This efficiency is close to pie/4 or 78% when the peak value of the output element half-sinusoid if achieves its maximum value Imax.
Its major advantage is its increased efficiency thus allowing considerable improvement in radio talk-time. That is when Ic = 0 for half cycle the output voltage is the tightest.
Disadvantages is its little gain
Its biasing is as follows: I(q) is set close to zero. The drain can be kept the same as for class A operation, although if the bias point is selected so that VD is allowed to swing up to breakdown voltage at high levels, it must be reduced by Vp/2 compared to class -A operation. This is because the breakdown occurs between drain and the gate; as the gate voltage is reduced form - Vp/2 in class A to –Vp for lass-B; this pulls the drain- gate diode closer to break down.
The drain voltage is therefore reduced by the same amount to keep the differential voltage across the diode the same. As long as the drain is biased through an RF choke, the voltage at drain can “float” around its average bias value of VDD. The endpoints of class – B wave form are the same as those of class – A . Its average slope and optimum resistors are the same too. Currents and voltage are the same too.
Push-pull configuration
]in class-B amplifier, the harmonic components of the output current are short-circuited by a tank circuit at the load.
In microwave and RF power devices the tank circuit is often omitted because the harmonics tend to be short circuited by the device output capacitance.
Some distortion is taken in exchange of improved efficiency.
Class-AB amplifier
Defined by a conduction angle that lies between 180o and 360o and the device is switched off for a portion of a cycle when the input voltage swings sufficiently into cut off. It conducts somewhere between 50% and 100% of a cycle depending on the bias levels chosen. As a result, its efficiency and linearity are intermediate between class A and B amplifier. It is a positive current bias rather than negative.
Class – C amplifier (switching mode amplifier)
The gate bias is arranged to cause the transistor to conduct less than half the time. It is traditional to approximate these pulses by the top pieces of sinusoids to facilitate a direct analysis.
iD= IDC + irf sinwot, iD>o where the offset IDC which is analogous to bias current in a linear amplifier is actually negative for a class C amplifier. The overall drain current iD is always positive or zero. Here the transistor behaves at all times as a current source (high output impedance).
Max Efficiency =(2X-Sin2X)/4(SinX-XCosX)
This result to a very close to 100% efficiency as the conduction angle shrinks towards zero.
Class D Amplifiers
An active device controlled by current source is used as a switch since switch dissipates no power and therefore 100% efficiency theoretically. Like push-pull class B amplifier, the input connection guarantees that only one transistor is driven on at a given time with one transistor handling the positive half-cycles and the other the negative half cycles, but driven hard enough to make the transistor act like a switch.
Each primary terminal of the output transforms (T2) is alternately driven to ground yielding a square –wave voltage across the primary (and therefore across the secondary) winding. When one drain goes to zero volts, transformer action forces the other drain to a voltage of 2 Vdd. The output filter allows only the fundamental components of this square wave to flow into the load.
Disadvantages are that the inclusion of a transformer makes the device bulky. And only functions well only at frequencies below transformer frequency.
CLASS E AMPLIFIERS
Though similar to class B or F amplifiers due to its 180o conduction angle, between saturation and cutoff, It uses switching principle and thus loosing its analog relationship between the input and output.
Modeled as a switch in parallel with the device output capacitance, that can be supplemented by an additional shunt capacitance. Total drain or collector current is then alternately steered between the device saturation resistance (i.e. the closed or on switch).
The device output current source is assumed Zero during the off half-cycle.
With 50% a duty cycle, extrinsic drain load at the fundamental frequency that provides the class-E wave-forms is inductive. And is independent of both the input and level and drain supply voltage. At microwave frequencies, the nonlinear nature of the intrinsic component calculated of this optimum load somewhat difficult.
Therefore ZL =R(1+j1.1525)
CLASS F AMPLIFERS
Here, the output tank is tuned to resonance at the carrier frequency and is assumed to have a high enough Q to act as a shot circuit at all frequencies outside of the desired band width.
The length of the transmission line is chosen to be precisely a quarter – wavelength at the carrier frequency. That is the input impedance of such a line is proportional to the reciprocal of the termination impedance
Zin = Zo2
ZL
The drain sees an open circuit at all even harmonies of the carrier since the transmission line appears as some integer multiple of a half-wavelength at all even harmonics. Conversely, the drain sees and open circuit at all odd harmonics of the carrier because the tank appears as a open circuit. Transmission line appears as an odd multiple of a quarter – wavelength and therefore provides a net reciprocation of the load impedance.
VDS = (4/3.14) 2VAD
Po = [(4/3.14) VDD][4/3.14 X VDD]/ 2R
This power amplifier as a peak to peak value which exceeds the totaT VDS swing due to Fourier transformation.
It has a high efficiency than all, up to 100% it also as a substantially better normalized power-handling capability because the maximum voltage is just twice the supply.
References
The design of CMOS Radio Frequency integrated circuits by Thomas H. Lee and
RF circuit design for modern wireless systems by rowan Gilmore and less bessser
Classes of amplifiers class A, B, AB, C, D, E and F
Class A
This circuit permits a simultaneous large voltage and current swing at the output of the device.
The circuit will always be on in this kind of amplifier unless some other switching circuit is added. Biasing is at the midway where current swing will be I max/2
Power efficiency is always 50% or less and cannot go beyond that amount.
Temperature is also another concern that the device may not be overheated.
iD = IQ + I peak cos not
vD = Vcc + I PEAK RL cos lot
PRF = I PEAK 2 RL
2
Effi = I PEAK 2 RL and PDISS = Pdc - PRF
2 IQ Vcc
The conductor angle of class A amplifier is 360o or 2 radians.
It is a larger gain compared to the rest of amplifiers
CLASS – B amplifier.
With a conductor angle of 180o or 3.14radians the circuit is independent of drive level.
When Vin exceeds a threshold value (Vo) the output current (Io) = G (Vin – Vo) and when it falls below threshold, Io = O
If G is trasnconductance and Vo is the bias voltage
Vin = Vb + Vicos wt
When the amplifier is on the output current mirrors he peaks of the inoput sinusoidal voltage .
The peak of the sine wave tips of the Io is just the trasconductance times the amount by which the input volatage exceeds the threshold that is
Ip=(Vi – Vx) G
Io(t) =IP/3.14 + IP/2 coswt +2Ip/3Pie cos 2wt – (2Ip/15pie) cos 4w + ----
Pdc = VccIp/pie
PRF = VPEAK IPEAK/2
This efficiency is close to pie/4 or 78% when the peak value of the output element half-sinusoid if achieves its maximum value Imax.
Its major advantage is its increased efficiency thus allowing considerable improvement in radio talk-time. That is when Ic = 0 for half cycle the output voltage is the tightest.
Disadvantages is its little gain
Its biasing is as follows: I(q) is set close to zero. The drain can be kept the same as for class A operation, although if the bias point is selected so that VD is allowed to swing up to breakdown voltage at high levels, it must be reduced by Vp/2 compared to class -A operation. This is because the breakdown occurs between drain and the gate; as the gate voltage is reduced form - Vp/2 in class A to –Vp for lass-B; this pulls the drain- gate diode closer to break down.
The drain voltage is therefore reduced by the same amount to keep the differential voltage across the diode the same. As long as the drain is biased through an RF choke, the voltage at drain can “float” around its average bias value of VDD. The endpoints of class – B wave form are the same as those of class – A . Its average slope and optimum resistors are the same too. Currents and voltage are the same too.
Push-pull configuration
]in class-B amplifier, the harmonic components of the output current are short-circuited by a tank circuit at the load.
In microwave and RF power devices the tank circuit is often omitted because the harmonics tend to be short circuited by the device output capacitance.
Some distortion is taken in exchange of improved efficiency.
Class-AB amplifier
Defined by a conduction angle that lies between 180o and 360o and the device is switched off for a portion of a cycle when the input voltage swings sufficiently into cut off. It conducts somewhere between 50% and 100% of a cycle depending on the bias levels chosen. As a result, its efficiency and linearity are intermediate between class A and B amplifier. It is a positive current bias rather than negative.
Class – C amplifier (switching mode amplifier)
The gate bias is arranged to cause the transistor to conduct less than half the time. It is traditional to approximate these pulses by the top pieces of sinusoids to facilitate a direct analysis.
iD= IDC + irf sinwot, iD>o where the offset IDC which is analogous to bias current in a linear amplifier is actually negative for a class C amplifier. The overall drain current iD is always positive or zero. Here the transistor behaves at all times as a current source (high output impedance).
Max Efficiency =(2X-Sin2X)/4(SinX-XCosX)
This result to a very close to 100% efficiency as the conduction angle shrinks towards zero.
Class D Amplifiers
An active device controlled by current source is used as a switch since switch dissipates no power and therefore 100% efficiency theoretically. Like push-pull class B amplifier, the input connection guarantees that only one transistor is driven on at a given time with one transistor handling the positive half-cycles and the other the negative half cycles, but driven hard enough to make the transistor act like a switch.
Each primary terminal of the output transforms (T2) is alternately driven to ground yielding a square –wave voltage across the primary (and therefore across the secondary) winding. When one drain goes to zero volts, transformer action forces the other drain to a voltage of 2 Vdd. The output filter allows only the fundamental components of this square wave to flow into the load.
Disadvantages are that the inclusion of a transformer makes the device bulky. And only functions well only at frequencies below transformer frequency.
CLASS E AMPLIFIERS
Though similar to class B or F amplifiers due to its 180o conduction angle, between saturation and cutoff, It uses switching principle and thus loosing its analog relationship between the input and output.
Modeled as a switch in parallel with the device output capacitance, that can be supplemented by an additional shunt capacitance. Total drain or collector current is then alternately steered between the device saturation resistance (i.e. the closed or on switch).
The device output current source is assumed Zero during the off half-cycle.
With 50% a duty cycle, extrinsic drain load at the fundamental frequency that provides the class-E wave-forms is inductive. And is independent of both the input and level and drain supply voltage. At microwave frequencies, the nonlinear nature of the intrinsic component calculated of this optimum load somewhat difficult.
Therefore ZL =R(1+j1.1525)
CLASS F AMPLIFERS
Here, the output tank is tuned to resonance at the carrier frequency and is assumed to have a high enough Q to act as a shot circuit at all frequencies outside of the desired band width.
The length of the transmission line is chosen to be precisely a quarter – wavelength at the carrier frequency. That is the input impedance of such a line is proportional to the reciprocal of the termination impedance
Zin = Zo2
ZL
The drain sees an open circuit at all even harmonies of the carrier since the transmission line appears as some integer multiple of a half-wavelength at all even harmonics. Conversely, the drain sees and open circuit at all odd harmonics of the carrier because the tank appears as a open circuit. Transmission line appears as an odd multiple of a quarter – wavelength and therefore provides a net reciprocation of the load impedance.
VDS = (4/3.14) 2VAD
Po = [(4/3.14) VDD][4/3.14 X VDD]/ 2R
This power amplifier as a peak to peak value which exceeds the totaT VDS swing due to Fourier transformation.
It has a high efficiency than all, up to 100% it also as a substantially better normalized power-handling capability because the maximum voltage is just twice the supply.
References
The design of CMOS Radio Frequency integrated circuits by Thomas H. Lee and
RF circuit design for modern wireless systems by rowan Gilmore and less bessser
Saturday, November 17, 2007
9 TYPES OF ANTENNAS
TYPES ANTENNAS
4 arm conical spiral
alford loop
aperture synthesis
array
axial mode helix
biconical w/polarizer
biconical
cavity backed circuit fed slot
cavity backed spiral
circular loop
conical spiral
corner reflector
dipole array, linear
dipole
discone
dual polarized sinuous
guide fed slot
helix, normal mode
helix, axial mode
horn
linear dipole array
log periodic
loop, circular
loop, alfred
loop, square
luneberg lens
microstrip patch
monopole
normal mode helix
parabolic
patch
reflector
rhombic
sinuous, dual polarized
slot, guide fed
slot, cavity backed
spiral, 4 arm conical
spiral, conical
spiral, cavity backed
square loop
vee
yagi
The Yagi antenna is narrow band, designed to work on only one channel or FM. It has the best gain for its size, and a correspondingly narrow main lobe (beam). If you need the highest gain, or to discriminate against an interfering signal 20-40 degrees azimuth off the desired signal, use a Yagi.
Omni. This antenna, sold for FM radio, is a bent folded dipole. It is advertised a an Omni, but only approximates omnidirectional reception.
A helical wire can have axial or broadside to axis radiation. Helix antennas are used for every VHF, UHF and microwave purpose from point to point to TV broadcast.
The supersturnstile. Take the turnstile used for omnidirectional reception, stretch the wires into vertical sheets, and nick the middle of the sheet into a sort of vertical bow tie, and you get the broad band antenna common to VHF TV broadcasting. O, yes, you can think of these things as slot type antenas also, since they have a vertical slot between the two batwings.
Rohmbic;Wire in the shape of a rhomboid makes a long wire into a high gain precision antenna.
RADIATION PATTERNS
The radiation pattern is a graphical depiction of the relative field strength transmitted from or received by the antenna. Antenna radiation patterns are taken at one frequency, one polarization, and one plane cut. The patterns are usually presented in polar or rectilinear form with a dB strength scale. Patterns are normalized to the maximum graph value, 0 dB, and a directivity is given for the antenna. This means that if the side lobe level from the radiation pattern were down -13 dB, and the directivity of the antenna was 4 dB, then the sidelobe gain would be -9 dB.
FREQUENCY / PHASE EFFECTS OF ANTENNAS
The radiation patterns of the antennas presented in the previous section are for antenna geometries most commonly used. The antenna should be viewed as a matching network that takes the power from a transmission line (50 ohm, for example), and matches it to the free space "impedance" of 377 ohms. The most critical parameter is the change of VSWR with frequency. The pattern usually does not vary much from acceptable to the start of unacceptable VSWRs (> 2:1). For a given physical antenna geometric size, the actual radiation pattern varies with frequency.
4 arm conical spiral
alford loop
aperture synthesis
array
axial mode helix
biconical w/polarizer
biconical
cavity backed circuit fed slot
cavity backed spiral
circular loop
conical spiral
corner reflector
dipole array, linear
dipole
discone
dual polarized sinuous
guide fed slot
helix, normal mode
helix, axial mode
horn
linear dipole array
log periodic
loop, circular
loop, alfred
loop, square
luneberg lens
microstrip patch
monopole
normal mode helix
parabolic
patch
reflector
rhombic
sinuous, dual polarized
slot, guide fed
slot, cavity backed
spiral, 4 arm conical
spiral, conical
spiral, cavity backed
square loop
vee
yagi
The Yagi antenna is narrow band, designed to work on only one channel or FM. It has the best gain for its size, and a correspondingly narrow main lobe (beam). If you need the highest gain, or to discriminate against an interfering signal 20-40 degrees azimuth off the desired signal, use a Yagi.
Omni. This antenna, sold for FM radio, is a bent folded dipole. It is advertised a an Omni, but only approximates omnidirectional reception.
A helical wire can have axial or broadside to axis radiation. Helix antennas are used for every VHF, UHF and microwave purpose from point to point to TV broadcast.
The supersturnstile. Take the turnstile used for omnidirectional reception, stretch the wires into vertical sheets, and nick the middle of the sheet into a sort of vertical bow tie, and you get the broad band antenna common to VHF TV broadcasting. O, yes, you can think of these things as slot type antenas also, since they have a vertical slot between the two batwings.
Rohmbic;Wire in the shape of a rhomboid makes a long wire into a high gain precision antenna.
RADIATION PATTERNS
The radiation pattern is a graphical depiction of the relative field strength transmitted from or received by the antenna. Antenna radiation patterns are taken at one frequency, one polarization, and one plane cut. The patterns are usually presented in polar or rectilinear form with a dB strength scale. Patterns are normalized to the maximum graph value, 0 dB, and a directivity is given for the antenna. This means that if the side lobe level from the radiation pattern were down -13 dB, and the directivity of the antenna was 4 dB, then the sidelobe gain would be -9 dB.
FREQUENCY / PHASE EFFECTS OF ANTENNAS
The radiation patterns of the antennas presented in the previous section are for antenna geometries most commonly used. The antenna should be viewed as a matching network that takes the power from a transmission line (50 ohm, for example), and matches it to the free space "impedance" of 377 ohms. The most critical parameter is the change of VSWR with frequency. The pattern usually does not vary much from acceptable to the start of unacceptable VSWRs (> 2:1). For a given physical antenna geometric size, the actual radiation pattern varies with frequency.
Sunday, November 11, 2007
6 ACTIVE RF SEMICONDUCTOR DEVICES
ACTIVE RF SEMICONDUCTOR DEVICES.
This are active semiconductors which when measured in a 50ohms terminating impedances at the source and load, the device itself will not be affected by changes in the input or output voltages or currents that may result with the use of other values of impedances at the terminals. This assumption underpins the entire linear design when we represent active device by a matrix formulation such as Y – or S – parameters.
It is assumed that the device is independent of the circuit in which it is embedded.
1) Two-port device models are made of GaAs MESFET
In this device, current is the function of the drain – source voltage.
2) The silicon bipolar transistor .
It is the first two-port device used for solid – state RF-design for RF frequencies lower than 1GHZ.
3) Others are the HBT (Heterojunction Bipolar Transistor). The Gummel-poon model transistor considers the number of additional features:
- Low current effects resulting from additional base current due to combination of a minority carriers in the bass.
- High level injection; occurs with excess majority carriers spill over from the base to collector.
- Base-width modulation – effective width of the base through which the electrons must transit is increased when forward bias on either of the junction increases.
- The Ac model parameters to account for change aggregation within the device.
4) The heterojuction bipolar transistor
- Is a high speed transistor; with better high frequency performance
The high-electron mobility transistor (HEMT) made of ALGaAs layers.
With high gain and extended frequency performance 200GHZ range. This excellent low- noise properties result from their high transconductance and good electron mobility. Off-the-shelf HemTs with 0.6dB and associated gain of 12dB at 15GHZ are available.
5) Silicon Ldmos and Cmos technologies
This are Rf intergrated circuits where synchronous digital hierarchy (SDH) operate up to 10Gbps and wireless LANS at 100Mbps.
LDmos are meant for GSM cellular system for its power amplification for upto 2GHZ and can also be used for power switching application at lower frequencies.
6) Others are the schottky diodes.
The pin diodes, which are used for high frequency switches and variable resistors.
Varector diode – Is capacitive under reverse bias.
7) IMPATT-diode – IMPact Avalanche and transistor Time which is a time diode.
8) Tunnel diode
9) TRAPPATT, BARRITT and Gunn diodes Trapped plasma Avalanche Triggered Transit – High efficiency upto 75%
BARRier Injection Transit Time has low efficiency of 5% to less 1 and is commonly used in RADAR mixed and detectors circuits.
Ref: practical RF CIRCUIT DESIGN FOR MODERN WIRELESS SYSTEM. Volume Ii by ROWAN GILMORE & LEE BESSER
This are active semiconductors which when measured in a 50ohms terminating impedances at the source and load, the device itself will not be affected by changes in the input or output voltages or currents that may result with the use of other values of impedances at the terminals. This assumption underpins the entire linear design when we represent active device by a matrix formulation such as Y – or S – parameters.
It is assumed that the device is independent of the circuit in which it is embedded.
1) Two-port device models are made of GaAs MESFET
In this device, current is the function of the drain – source voltage.
2) The silicon bipolar transistor .
It is the first two-port device used for solid – state RF-design for RF frequencies lower than 1GHZ.
3) Others are the HBT (Heterojunction Bipolar Transistor). The Gummel-poon model transistor considers the number of additional features:
- Low current effects resulting from additional base current due to combination of a minority carriers in the bass.
- High level injection; occurs with excess majority carriers spill over from the base to collector.
- Base-width modulation – effective width of the base through which the electrons must transit is increased when forward bias on either of the junction increases.
- The Ac model parameters to account for change aggregation within the device.
4) The heterojuction bipolar transistor
- Is a high speed transistor; with better high frequency performance
The high-electron mobility transistor (HEMT) made of ALGaAs layers.
With high gain and extended frequency performance 200GHZ range. This excellent low- noise properties result from their high transconductance and good electron mobility. Off-the-shelf HemTs with 0.6dB and associated gain of 12dB at 15GHZ are available.
5) Silicon Ldmos and Cmos technologies
This are Rf intergrated circuits where synchronous digital hierarchy (SDH) operate up to 10Gbps and wireless LANS at 100Mbps.
LDmos are meant for GSM cellular system for its power amplification for upto 2GHZ and can also be used for power switching application at lower frequencies.
6) Others are the schottky diodes.
The pin diodes, which are used for high frequency switches and variable resistors.
Varector diode – Is capacitive under reverse bias.
7) IMPATT-diode – IMPact Avalanche and transistor Time which is a time diode.
8) Tunnel diode
9) TRAPPATT, BARRITT and Gunn diodes Trapped plasma Avalanche Triggered Transit – High efficiency upto 75%
BARRier Injection Transit Time has low efficiency of 5% to less 1 and is commonly used in RADAR mixed and detectors circuits.
Ref: practical RF CIRCUIT DESIGN FOR MODERN WIRELESS SYSTEM. Volume Ii by ROWAN GILMORE & LEE BESSER
4 CELLULAR PHONES
BLOCK DIAGRAM OF A MOBILE PHONE
CIRCUIT DIAGRAM OF A MOBILE PHOHE
CIRCUIT DIAGRAM OF A MOBILE PHOHE
CELLULAR PHONES
An example of multi-mode/multi-band mobile phones with separate RF front end and down converters to IF, which is possibly a shared IF. The component used is the here is a SA1920 from Philips semiconductors, an RF front-end intended to covers the 900 and 1,900MHz wireless bands.
Designed with a 13GHz-fT Bicmos process and requires a 3.75 V dc supply.
It is intended for diverse systems as AMPs, GSM and PCs, without any modulation - specific functions because it covers two bands with many filtering between stages.
The low-band section contains a separate LNA and mixer that cover 869 – to 960MHz RF frequencies with an input IF between 100 and 125 MHZ.
The LNA has a noise figure of 1.7 dB and 17.5dB gain. The mixer has 9.5dB gain and an IIP3 of +5dBm. When cascaded, with a filter between them, the combined noise figure is 2.6dB.
The high – band sections contains an LNA and an image- reject mixer based on Gilbert cells that operate from 1,805 to 1,990MHZ. The two are internally cascaded, and together achieve 4.2 dB noise figure, 23.5dB gain and an IIP3 of 12.5Bm.
The high and low-band lo signals are fed from off-clip (pins 30/31). For the high band, the lo in – phase and quadrature signals are derived by two internal all pass networks. The IF output signals are internally shifted by 90o and recombined to realize image – rejection. Contain a separate broadband mixer block for use in transmitter chain (pin10)
It down converts the transmitted signal using the Lo as the receiver. This enables the transmitted, down converted IF channels (pin2/3) to be used in a closed – loop Cartesian transmitter to improve linearity.
Maxim integrated product (MAX 2338) is an RF front – end clip for mod AMPS/N-CDMA cellular phone or for other systems such as duel – band GSM. Like SA1920, converts RF to IF and contains separate LNA sections for both high (1930 to 1990 MHZ) and low (869 to 892MHZ) Rx band which are fed directly from the duplex following the antenna. The gain of LNA, is IIP3 from +5 to 18dBm. With a high linearity mode for higher power CDMA signals, that can only be switched on when necessary. The mixer uses an off- clip Lo at around 2,150MHZ that can be divided by a factor of two for the lower Band to have a IF of around 183MHZ to be used. The clip operates with a 3V dc supply.
Ref: practical RF CIRCUIT DESIGN FOR MODERN WIRELESS SYSTEM. Volume Ii by ROWAN GILMORE & LEE BESSER
An example of multi-mode/multi-band mobile phones with separate RF front end and down converters to IF, which is possibly a shared IF. The component used is the here is a SA1920 from Philips semiconductors, an RF front-end intended to covers the 900 and 1,900MHz wireless bands.
Designed with a 13GHz-fT Bicmos process and requires a 3.75 V dc supply.
It is intended for diverse systems as AMPs, GSM and PCs, without any modulation - specific functions because it covers two bands with many filtering between stages.
The low-band section contains a separate LNA and mixer that cover 869 – to 960MHz RF frequencies with an input IF between 100 and 125 MHZ.
The LNA has a noise figure of 1.7 dB and 17.5dB gain. The mixer has 9.5dB gain and an IIP3 of +5dBm. When cascaded, with a filter between them, the combined noise figure is 2.6dB.
The high – band sections contains an LNA and an image- reject mixer based on Gilbert cells that operate from 1,805 to 1,990MHZ. The two are internally cascaded, and together achieve 4.2 dB noise figure, 23.5dB gain and an IIP3 of 12.5Bm.
The high and low-band lo signals are fed from off-clip (pins 30/31). For the high band, the lo in – phase and quadrature signals are derived by two internal all pass networks. The IF output signals are internally shifted by 90o and recombined to realize image – rejection. Contain a separate broadband mixer block for use in transmitter chain (pin10)
It down converts the transmitted signal using the Lo as the receiver. This enables the transmitted, down converted IF channels (pin2/3) to be used in a closed – loop Cartesian transmitter to improve linearity.
Maxim integrated product (MAX 2338) is an RF front – end clip for mod AMPS/N-CDMA cellular phone or for other systems such as duel – band GSM. Like SA1920, converts RF to IF and contains separate LNA sections for both high (1930 to 1990 MHZ) and low (869 to 892MHZ) Rx band which are fed directly from the duplex following the antenna. The gain of LNA, is IIP3 from +5 to 18dBm. With a high linearity mode for higher power CDMA signals, that can only be switched on when necessary. The mixer uses an off- clip Lo at around 2,150MHZ that can be divided by a factor of two for the lower Band to have a IF of around 183MHZ to be used. The clip operates with a 3V dc supply.
Ref: practical RF CIRCUIT DESIGN FOR MODERN WIRELESS SYSTEM. Volume Ii by ROWAN GILMORE & LEE BESSER
5 FILTER DESIGNS
Filters Designs
All designs of filters are either one of the following
A low pass filter
A High pass filter
A All pass filter
A Band pass filter
A Band – stop filter
Low pass filters are used for attenuating the undesired higher frequencies while letting the lower frequencies to passes through.
A High – pass filter is used to attenuate the lower undesired frequencies while allowing the high frequencies to pass.
All-pass filter passes all frequencies at the same gain. Its main use is to change the phase of the signal and as a phase – correction circuit.
A Band pass filter is a combination of low and high pass-filters where the low pass will alternate the undesired high frequencies and the high pass alternate the undesired low frequencies living a band of frequencies in between as a Bandwidth.
A Band stop filter passes all frequencies but attenuates a certain band in between (middle). Allows upper and lower frequencies to pass. This is double pole circuit or a second order filters.
The first three are first order circuit or single pole circuits.
Sallen –Key
It is the mostly widely known second-order topology filter. It requires a single op-amp, and four passive components.
With easy tuning, the circuit is a unity again and can change style to a unity gain Butterworth.
Multiple feedback (MFB)
It is a very versatile, low cost and easy to implement but calculations are somewhat complex.
Fliege filter
Has good control over the tuning and the Q style. The gain is fixed at two for low-pass and band-pass filters and unity for Notch.
Akerberg – Mossberg filter
Easiest to use from the rest. Easy to change the gain style of low –pass and high pass and the Q of band-pass and Notch filters.
Bi Quad
Only available in a low-pass and band-pass varieties. The low-pass filter is useful whenever simultaneous normal and inverted outputs are needed.
All designs of filters are either one of the following
A low pass filter
A High pass filter
A All pass filter
A Band pass filter
A Band – stop filter
Low pass filters are used for attenuating the undesired higher frequencies while letting the lower frequencies to passes through.
A High – pass filter is used to attenuate the lower undesired frequencies while allowing the high frequencies to pass.
All-pass filter passes all frequencies at the same gain. Its main use is to change the phase of the signal and as a phase – correction circuit.
A Band pass filter is a combination of low and high pass-filters where the low pass will alternate the undesired high frequencies and the high pass alternate the undesired low frequencies living a band of frequencies in between as a Bandwidth.
A Band stop filter passes all frequencies but attenuates a certain band in between (middle). Allows upper and lower frequencies to pass. This is double pole circuit or a second order filters.
The first three are first order circuit or single pole circuits.
Sallen –Key
It is the mostly widely known second-order topology filter. It requires a single op-amp, and four passive components.
With easy tuning, the circuit is a unity again and can change style to a unity gain Butterworth.
Multiple feedback (MFB)
It is a very versatile, low cost and easy to implement but calculations are somewhat complex.
Fliege filter
Has good control over the tuning and the Q style. The gain is fixed at two for low-pass and band-pass filters and unity for Notch.
Akerberg – Mossberg filter
Easiest to use from the rest. Easy to change the gain style of low –pass and high pass and the Q of band-pass and Notch filters.
Bi Quad
Only available in a low-pass and band-pass varieties. The low-pass filter is useful whenever simultaneous normal and inverted outputs are needed.
Wednesday, November 7, 2007
Monday, November 5, 2007
3.MICROWAVE SYSTEM
A microwave is signal measuring a wavelength of 30.05 cm or less which is converted to 984MHZ. This puts all the frequencies above 1GHZ under the same name (microwaves).The highest range of the microwave is 10 PetaHZ, which are light frequencies. But practical maximum range is 300 GHZ with a wavelength of 0.1 cm. It transmits very high power, very short duration pulse distance between two object that can be determined by measuring the time span for the signal of a known velocity after being reflected back.
The pulse generator sets the pulse width and the pulse repetition rate (tine between pulses) of the transmitted signal. Modulator turns on power oscillator for a given time at a rate determined by the pulse generator. The oscillator oscillates at the RF carrier frequency to send out short burst of high-frequency energy.
The HF and high power energy is carried by the waveguide to the horn antenna and parabolic reflector to concentrate energy into a narrow pencil beam to the target.
Transmit Receive (TR) tube short – circuits the waveguide going to the mixer so as to protect the diode mixer from high- energy pulse from power oscillator. The anti-transmit receive (ATR) box is gas – filled tube like TR but in series with waveguide that connects the power oscillator to the antenna. ATRs form a low – impedance path for power oscillator signal going to the antenna during high – energy pulse. It only becomes a high impedance at receive mode. Distance between ATR and TR must always be ¼ wavelength.
Echo box is used for testing the system when no targets are within range but turned far off carrier frequency during normal operation. A pulse is transmitted while the echo box is motor – tuned through resonance to indicate a return signal.
The mixer gets signal from the antennae and from the local oscillator too. The oscillator operates at a frequency higher than RF signal. The IF amp selects the difference frequency at about 30MHZ from the out put of the mixer. The IF has 5 Amplifying stages for a higher gain over 10MHZ bandwidth.
AFC is equivalent to phase-locked loop circuit. After the mixer acting as a comparator and amplified by IF circuit. The signal is then converted to DC in the AFC circuit relative to frequency change and is used to control the frequency of a VCO.
Video amplifier with wideband frequency response to accommodate multiple odd harmonics of the fundamental square wave modulating signal. The product of the video amplifier is used to intensely modulate the CRT monitor. The deflection oscillator generates a trapezoidal wave signal to be amplified by power amplifier.
The amplifier signal is then applied to deflection coil round the neck of the CRT
The synchronizing circuit notes each pulse from the generator and starts CRT sweep at the center of the display monitor as each pulse leaves transmitter.
The synchronizing circuit notes each pulse from the generator and starts CRT sweep at the center of the display monitor as each pulse leaves transmitter.
For full time – distance indication, Range markers are added to display the full adder.
Motor servo system controls the spread and position of the rotating antenna assembly.
Reference:
Electronic communications Modulation and Transmissions by Robert J Schoenbeck.
RF Circuits Design Wireless System Volume 3 By Gilmore Besser,
The Design of CMOS Radio frequency Integrated Circuits By Thomas H Lee.
And http:/wikipedia.org/wiki/transmissionline/
Dr. David J., Jefferies, School of electronics engineering, IT and Mathematics, University of Survey England.
Motor servo system controls the spread and position of the rotating antenna assembly.
Reference:
Electronic communications Modulation and Transmissions by Robert J Schoenbeck.
RF Circuits Design Wireless System Volume 3 By Gilmore Besser,
The Design of CMOS Radio frequency Integrated Circuits By Thomas H Lee.
And http:/wikipedia.org/wiki/transmissionline/
Dr. David J., Jefferies, School of electronics engineering, IT and Mathematics, University of Survey England.
2.SMITH CHART
This is a circular slide rule graph that enables exact calculations of transmission line matching. It was developed around 1939 by P.H Smith and has become very useful to date in it we are able to match transformers for complex load impedance and correct the electronic enemy of attenuations within the transmission lines. It helps in the design of the antennas.
The chart constitutes the following
The chart constitutes the following
1.Pure resistance (or Zero reactance) line.
2.Two circles sets for reactance XL and Xc.
3.Two wavelength scales.
4.The reflection co- efficient angle scale.
5.The reflection co- efficient magnitude scale.
6.The dB of loss scale.
4.The reflection co- efficient angle scale.
5.The reflection co- efficient magnitude scale.
6.The dB of loss scale.
I. PURE RESISTANCE LINE.
It lies horizontally across the chart passing through the prime centre of the graph
extending in both directions to the perimeter of the chart called zero reactance where it is
calibrated from zero; on the left, to infinity, on the right. The value of l is at the graph's
center.
II. REACTANCE CIRCLES (ARCS).
The area above horizontal line is reserved for inductive reactance while the area at
the lower half of the chart is reserved for capacitive reactance. This explains why the horizontal line is called the zero reactance line. The reactance circle sets are a series of eccentric cycles above and below the horizontal line and tangential to the point of infinity. Although the reactance are full-circles, values only at the portion of a circle that falls inside the resistance circle R=0 is included on the Smith chart. The point is that reactance values greater than 1= l+(jx or-jx) will only be located in an area smaller than 1/4 of the total smith chart area. The upper right Quadrant is for values of +jx and lower right for values of –jx values. But first the values for resistance are printed on the chart along the zero reactance line and along part of each X= 1 arc. Values of reactance are printed around the perimeter of the R=0 circle and again along part of the R=l circle.
III. WAVE LENGTH SCALES.
These are two scales around the outside edge of the chart. They both start at the left of the
chart on the Zero reactance line. They advance in clockwise direction only to make half
Wavelength in one full revolution as 0 mark represents starting point and ending point.
This is labeled "wavelengths towards the generator". The one half wavelength measures are used because the transmission lines patterns repeat themselves every half wavelength.
The second inner scale labeled "wavelength toward the load" advances in
Anticlockwise direction. The choice of use of a scale depends on the information known
and what information is to be determined. Measure of one-quarter wavelength toward the
generator and that of one-quarter wavelength toward the load are both at the generator and one quarter wavelength toward the same point (extreme right). The two wavelength scales
are on separate slip rings and are freely positioned anywhere around the perimeter of the
chart
are on separate slip rings and are freely positioned anywhere around the perimeter of the
chart
IV. REFLECTION COEFFICIENT.
The third scale from the edge is marked Angle of reflection coefficient in degrees starts
from left to right with positive 180° represented at the upper half while negative angles
represented at lower half of the chart.
V. REFLECTION MAGNITUDE.
Identified as radially scaled parameters. On the smith circular slide rule are scales on a clear bar attached to the center of the calculator and is free to rotate around the chart. The two scales of interests for the reflection coefficient magnitude, at the upper right and the dB loss, found on the upper left. The scales are also applied as the need arises and uses of the chart are established.
NORMALIZED IMPEDANCES.
This is a chart that has the R=l circle passing through the primary center and is made to
process all values of impedance values smaller than 50ohms. Charts would have the R=50 circles passing through the prime center. All impedance values smaller than R=50 ohms and would have be to the left of the center. But the normalized reference impedance chart is designed to represent all values of load impedance. The conversion from real-life load impedance is executed by dividing the characteristics impedance.
Zn=Z1Z0 e.g. 60j80 ohms=>60/50=1.2 and 80/50=1.6
Normalized impedance = 1.2 + j1.6ohms
Standing wave Ratio circle
When a circle on the smith Chart where the prime center (R=l, X=0) as a pivot point and
Zn as a point on the circumference, the circle is called the standing wave ratio-circle.
1) Numerical value of the standing wave ratio, Is the point where the circle crosses the
Zero reactance line to the right.
2) Value of the load Zn is located on this circle; SWR circle is a plot of the impedance on the line at every point along the length of the line.
3) SWR circle as the location of the maximum voltage of the standing wave (Emax) at
X=0 in wavelengths from the load (Znmax) on the line, in wavelengths from the load.
4) Where the SWR circle crosses the zero reactance line to the left of center represents
the location along the line where Emin and Zmax are found.
The load line
This is a line drawn from the prime center of the chart and passes through Zn and extends out past the wavelength scales cutting through the wavelength towards the generator.
It moves along the outer wavelength scale to the point where it intersects the Zero reactance line wavelengths. This wavelength difference is the distance from the load to where the standing wave voltage is maximum.
The SWR circle crosses clock wisely the Zero reactance line left of center where the circle (SWR) circle crosses the X=0 line on the right sides gives the SWR.
Radius of the circle is determined by the point Zn and R=l as the center of pivot,
Zn, Yn (admittance) and Bn (susceptance) lie on the SWR line (circle) with Zn being the inverse of Yn. To find Bn move clockwise from Yn to a point where SWR circle first crosses the R=l circle and that is the point Bn.
Matching load impendence
Inductors and capacitors are the best components as far as load impendence matches are concerned. This is because resistors siphon off 33% of power intended for the load.
When put in parallel 30% of load power is dissipated when connected in series.
Step one is the normalization of the load impendence by dividing it by the
characteristics impendence of the line.
Zn = Zl/Zo e.g. If ZL=120=80 ~ and Zo = 100~(Transmission line)
= 120 = j80
100
The load line is changed to a value that can be plotted an the universal graph(chart)
The value read from the graph and renormalized to a real life impendence value by multiplying the chart value by the line impendence.
Step two is plotting of the normalized values onto the graph and drawing the S.W.R circle. The load line joining the R=l and Zn is extended in the inverse direction to find the admittance of the load. That is Zn divided by any convenient Z value. Plot Zn on the chart, draw a circle and a load line, find the normalized admittance and then multiply the normalized admittance by the selected Z value. Practically, a section of the same transmission line to is be used to form a capacitor or inductor and is connected in parallel with line being matched. This section is called a matching stub. The smith chart determines the size and placement of the matching stub that will cause an irregular load impendence to match the line impendence.
Other uses of smith chat include the uses of an instrument called slotted line. Minimum and maximum voltage of the maximum voltage of the standing wave can be measured with great accuracy using a slotted line.
SWR = E max / E min
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