Motorola Gm328 Gm338 Gm398 Detailed 6804112j18 E Manual
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Transmitter Power Amplifier (PA) 40 W2-5 3.5 Bi-Directional Coupler The Bi-directional coupler is a microstrip printed circuit, which couples a small amount of the forward and reverse power of the RF power from Q4441. The coupled signal is rectified to an output power proportional dc voltage by the diodes D4451 & D4452 and sent to the RFIN of the PCIC. The PCIC controls the gain of stage U4401 as necessary to hold this voltage constant. This ensures the forward power out of the radio is held to a constant value. 3.6 Antenna Switch The antenna switch utilizes the existing dc feed (A+) to the last stage device (Q4441). Basic operation is to have both PIN diodes D4471 and D4472 turns on during key-up by forward biasing them. It is achieve by pulling down the voltage at the cathode end of D4472 to around 11.8V (0.7V drop across each diode). The current through the diodes needs to be set around 80mA to fully open the transmit path through resistor R4496. Q4472 is a current source controlled by Q4471 and is eventually connected to pin ANO of PCIC. VR4471 ensures the voltage at the resistor R4511 never exceeds 5.6V. 3.7 Harmonic Filter Inductors L4491, L4492, L4493 and capacitors C4448, C4493,C4494, C4496 and C4498 form a low-pass filter to attenuate harmonic energy from the transmitter. R4491 is used to drain any electrostatic charges that might otherwise build up on the antenna. The harmonic filter also prevents high level RF signals above the receiver passband from reaching the receiver circuits, improving spurious response rejection. 3.8 Power Control The transmitter uses the Power Control IC (PCIC, U4501) to control the power output of the radio. A portion of the forward RF power from the transmitter is sampled by the bi-directional coupler and rectified, to provide a dc voltage to the RFIN port of the PCIC (pin 1) which is proportional to the sampled RF power. The PCIC has internal digital to analog converters (DACs) which provide the reference voltage of the control loop. The reference voltage level is programmable through the SPI line of the PCIC. This reference voltage is proportional to the desired power setting of the transmitter, and is factory programmed at several points across the frequency range of the transmitter to offset frequency response variations of the transmitter’s power detector circuits.
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2-6Frequency Synthesis The PCIC provides a dc output voltage at pin 4 (INT) and applied as CNTLVLTG to the power-adjust input pin of the first transmitter stage U4401. This adjusts the transmitter power output to the intended value. Variations in forward or reflected transmitter power cause the dc voltage at pin 1 to change, and the PCIC adjusts the control voltage above or below its nominal value to raise or lower output power. Capacitors C4502-4, in conjunction with resistors and integrators within the PCIC, control the transmitter power-rise (key-up) and power-decay (de-key) characteristic to minimize splatter into adjacent channels. U4502 is a temperature-sensing device, which monitors the circuit board temperature in the vicinity of the transmitter driver and final devices, and provides a dc voltage to the PCIC (TEMP, pin 29) proportional to temperature. If the dc voltage produced exceeds the set threshold in the PCIC, the transmitter output power is reduced so as to reduce the transmitter temperature. 4.0 Frequency Synthesis The synthesizer subsystem consists of the reference oscillator (Y4261 or Y4262), the low voltage fractional-N synthesizer (LVFRAC-N, U4201), and the Voltage Controlled Oscillator VCO. 4.1 Reference Oscillator The reference oscillator (Y4262) contains a temperature compensated crystal oscillator with a frequency of 16.8 MHz. An Analog-to-Digital (A/D) converter internal to U4201 (LVFRAC-N) and controlled by the µP via serial interface (SRL) sets the voltage at the warp output of U4201, pin 25 to set the frequency of the oscillator. The output of the oscillator (pin 3 of Y4262) is applied to pin 23 (XTAL1) of U4201 via an RC series combination. In applications where less frequency stability is required the oscillator inside U4201 is used along with an external crystal Y4261, varactor diode D4261, C4261, C4262 and R4262. In this case, Y4262, R4263, C4235 and C4251 are not used. When Y4262 is used, Y4261, D4261, C4261, C4262 and R4262 are not used, and C4263 is increased to 0.1 uF.
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Frequency Synthesis2-7 4.2 Fractional-N Synthesizer The LVFRAC-N synthesizer IC (U4201) consists of a pre-scaler, a programmable loop divider, control divider logic, a phase detector, a charge pump, an A/D converter for low frequency digital modulation, a balanced attenuator to balance the high frequency analog modulation and low frequency digital modulation, a 13V positive voltage multiplier, a serial interface for control, and finally a super filter for the regulated 5 volts. A voltage of 5V applied to the super filter input (U4201 pin 30) supplies an output voltage of 4.5 Vdc (VSF) at pin 28. It supplies the VCO, VCO modulation bias circuit (via R4322) and the synthesizer charge pump resistor network (R4251, R4252). The synthesizer supply voltage is provided by the 5V regulator U4211. In order to generate a high voltage to supply the phase detector (charge pump) output stage at pin VCP (U5701-32), a voltage of 13 Vdc is being generated by the positive voltage multiplier circuitry (D4201, C4202, C4203). This voltage multiplier is basically a diode capacitor network driven by two signals (1.05MHz) 180 degrees out of phase (U4201-14 and -15). Figure 2-3 UHF Synthesizer Block Diagram Output LOCK (U4201-4) provides information about the lock status of the synthesizer loop. A high level at this output indicates a stable loop. IC U4201 provides the 16.8 MHz reference frequency at pin 19. The serial interface (SRL) is connected to the µP via the data line DATA (U4201-7), clock line CLK (U4201-8), and chip enable line CSX (U4201-9). DATA CLK CEX MODIN VCC, DC5V XTAL1 XTAL2 WARP PREIN VCP REFERENCE OSCILLATOR VOLTAGE MULTIPLIER DATA (U0101 PIN 100) CLOCK (U0101 PIN 1) CSX (U0101 PIN 2) MOD IN (U0221 PIN 40) +5V (U4211 PIN 1)7 8 9 10 13, 30 23 24 25 32 47 VMULT2 VMULT1BIAS1 SFOUTAUX3 AUX4 IADAPTIOUTGND FREFOUTLOCK4 19 6, 22, 33, 44 43 45 3 2 28 14 1540FILTERED 5VSTEERING LOCK (U0101 PIN 56) PRESCALER INFREF (U0221 PIN 34) 39 BIAS2 41 48 5, 20, 34, 36 +5V (U4211 PIN 1) AUX1 VDD, DC5VMODOUT U4201 LOW VOLTAGEFRACTIONAL-N SYNTHESIZER AUX21 (NU) BWSELECTVCO Bias TRB To IF SectionTX RF INJECTION (1ST STAGE OF PA)LO RF INJECTION VOLTAGE CONTROLLED OSCILLATORLINE 2-POLE LOOP FILTER
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2-8Frequency Synthesis 4.3 Voltage Controlled Oscillator (VCO) The Voltage Controlled Oscillator (VCO) consists of the VCO buffer IC (VCOBIC, U4301), the TX and RX tank circuits, the external RX buffer stages, and the modulation circuits. The VCOBIC together with Fractional-N synthesizer (U4201) generates the required frequencies in both transmit and receive modes. The TRB line (U4301 pin 19) determines which tank circuits and internal buffers are to be enabled. A high level on TRB enables TX tank and TX output (pin 10), and a low enables RX tank and RX output (pin 8). A sample of the signal from the enabled output is routed from U4301 pin 12 (PRESC_OUT), via a low pass filter, to pin 32 of U4201 (PREIN). A steering line voltage (VCTRL) between 3.0V and 10.0V at varactor diode CR4311 will tune the full TX frequency range (TXINJ) from 403 MHz to 470 MHz, and at varactor diodes CR4301, CR4302 and CR4303 will tune the full RX frequency range (RXINJ) from 358 MHz to 425 MHz. The tank circuits uses the Hartley configuration for wider bandwidth. For the RX tank circuit, an external transistor Q4301 is used in conjunction with the internal transistor for better side-band noise. Figure 2-4 UHF VCO Block Diagram The external RX buffers (Q4332) are enabled by a high at U4201 pin 3 (AUX4) via transistor switch Q4333. In TX mode the modulation signal (VCOMOD) from the LVFRAC-N synthesizer IC (U4201 pin41) is applied to the modulation circuits CR4321, R4321, R4322 and C4324. These modulate the TX VCO frequency via coupling capacitor C4321. Varactor CR4321 is biased for linearity from the VSF. Presc RX TXMatching NetworkLow Pass Filter Attenuator Pin8 Pin14 Pin10(U4201 Pin28) VCC Buffers TX RF Injection U4201 Pin 32 AUX3 (U4201 Pin2) Prescaler Out Pin 12 Pin 19 Pin 20 TX/RX/BS Switching Network U4301 VCOBIC Rx Active Bias Tx Active Bias Pin2 Rx-I adjustPin1 Tx-I adjustPins 9,11,17 Pin18Vsens Circuit Pin15Pin16 RX VCO Circuit TX VCO Circuit RX Tank TX TankPin7 Vcc-Superfilter Collector/RF in Pin4 Pin5 Pin6 RX TX (U4201 Pin28)Rx-SW Tx-SW Vcc-Logic (U4201 Pin28) Steer Line Voltage (VCTRL)Pin13 Pin3TRB IN LO RF INJECTION Q4301 Q4332
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Frequency Synthesis2-9 4.4 Synthesizer Operation The complete synthesizer subsystem comprises mainly of a low voltage FRAC-N (LVFRACN) IC, Reference Oscillator (crystal oscillator with temperature compensation), charge pump circuits, loop filter circuits, and dc supply. The output signal (PRESC_OUT) of the VCOBIC (U4301, pin12) is fed to of U4201, pin 32 (PREIN) via a low pass filter (C4229,L4225,C4226) which attenuates harmonics and provides correct level to close the synthesizer loop. The pre-scaler in the synthesizer (U4201) is basically a dual modulus pre-scaler with selectable divider ratios. The divider ratio of the pre-scaler is controlled by the loop divider, which in turn receives its inputs via the SRL. The output of the pre-scaler is applied to the loop divider. The output of the loop divider is connected to the phase detector, which compares the loop divider´s output signal with the reference signal.The reference signal is generated by dividing down the signal of the reference oscillator (Y4261 or Y4262). The output signal of the phase detector is a pulsed dc signal which is routed to the charge pump. The charge pump outputs a current at pin 43 of U4201 (IOUT). The loop filter (which consists of R4221-R4223, C4221-C4225,L4221) transforms this current into a voltage that is applied to the varactor diodes CR4311 for transmit, CR4301, CR4302 & CR4303 for receive and alters the output frequency of the VCO.The current can be set to a value fixed in the LVFRAC-N IC or to a value determined by the currents flowing into BIAS 1 (U4201-40) or BIAS 2 (U4201-39). The currents are set by the value of R4251 or R4252 respectively. The selection of the three different bias sources is done by software programming. To reduce synthesizer lock time when new frequency data has been loaded into the synthesizer the magnitude of the loop current is increased by enabling the IADAPT (U4201-45) for a certain software programmable time (Adapt Mode). The adapt mode timer is started by a low to high transient of the CSX line. When the synthesizer is within the lock range the current is determined only by the resistors connected to BIAS 1, BIAS 2, or the internal current source. A settled synthesizer loop is indicated by a high level of signal LOCK (U4201-4). LOCK (U4201-4) signal is routed to one of the µP´s ADCs input U101-56. From the voltage the µP determines whether LOCK is active. In order to modulate the PLL the two spot modulation method is utilized Via pin 10 (MODIN) on U4201. The audio signal is applied to both the A/D converter (low frequency path) as well as the balanced attenuator (high frequency path). The A/D converter converts the low frequency analog modulating signal into a digital code which is applied to the loop divider, thereby causing the carrier to deviate. The balance attenuator is used to adjust the VCO’s deviation sensitivity to high frequency modulating signals. The output of the balance attenuator is present at the MODOUT port (U4201- 41) and connected to the VCO modulation diode CR4321 via R4321, C4325.
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2-10Frequency Synthesis THIS PAGE INTENTIONALLY LEFT BLANK
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3-1 Section 3 TROUBLESHOOTING CHARTS 1.0 Troubleshooting Flow Chart for Receiver (Sheet 1 of 2) Bad SINAD Bad 20dB Quieting No Recovered AudioSTART Audio at pin 8 of U3101 ?Check Controller (in the case of no audio) OR ELSE go to “B” Ye s No Spray or inject 44.85MHz into XTAL Filter FL3101 Audio heard ?BYe s No Check 2nd LO (44.395MHz) at C3135 LO present ?BYe s Check voltages on U3101Biasing OK ? No No A Ye s Check Q3102 bias for faults Replace Q3102 Go to B Ye s No Check circuitry around U3101. Replace U3101 if defect Check circuitry around Y3101. Replace Y3101 if defectVoltages OK?
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3-2Troubleshooting Flow Chart for Receiver 1.1Troubleshooting Flow Chart for Receiver (Sheet 2 of 2) IF Signal at C3101? No RF Signal at T4051? RF Signal at C4015? No No RF Signal at C4025? No or Check harmonic filters L4491-L4493, C4492, J4401 and ant. switch D4471, D4472, L4472. Check filter between C4025 & C4009. Check tuning voltage at R4060. Inject RF into J4401 Is tuning voltage OK? No Ye s Check RF amp (Q4003) Stage. Check filter between C4015 & T4051. Ye s Check T4051, T4052, D4051, R4052, L4008. Ye s 1st LO level OK? Locked?Ye s Check FGU Ye s Trace IF signal from C3101 to Q3101. Check for bad XTAL filter. No Ye sIF signal at Q3102 collector? Before replacing U3101, check U3101 voltages. Ye s Check for 5VDC Is 9V3 present? Check Supply Voltage circuitry. Check U0611 and U0641. No No No Check U4501. Check varactor filter. NoYe s Ye s Ye s A A B weak RFRF Signal at C4009?
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Troubleshooting Flow Chart for 40W Transmitter 3-3 2.0 Troubleshooting Flow Chart for 40W Transmitter No Is Q4441 OK ? Ye s Is drive from VCO >+4dBm? NoIs voltage drop across R4497 >4.5V ?No Check Q4431 gate(open) and drain resistances (11kohm)NoCheck Q4421 gate(open) and drain resistances (11kohm)No Check PCIC_MOSBIAS_1 NoNo Change Q4573 START No power Is Vctrl there? Is Q4573 OK? Check voltage on pin 4 U4501 Check voltage on pin 5 U4501 Check R4422-5 and go back to top Troubleshoot ASFIC Check voltage on TP4531 Change PCIC Check R4409 & R4473 and go back to top Check MOSBIAS_2Check ASFIC Are D4471 & D4472 OK?Change D4471 & D4472 NoNo No NoNo Ye sYe sYe s Ye s Ye sYe s Ye s Ye s No NoCheck PCIC Ye s Change Q4421 Change Q4431 Ye s Change U4401 Ye sDo visual check on all components No Change Q4441 Troubleshoot VCO
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3-4Troubleshooting Flow Chart for Synthesizer 3.0 Troubleshooting Flow Chart for Synthesizer 5V at pin 6 of D4201 Is information from µP U0101 correct? Is U4201 Pin 47 at = 13VDC Is U4301 Pin 19 4.5 VDC in TX? (at VCO section) Start Vi s u a l check of the Board OK?Correct Problem Check 5V Regulator U4211 +5V at U4201 Pin’s 13 & 30? Is 16.8MHz Signal at U4201 Pin 19? Check Y4261, C4261, C4262, C4263, D4261 & R4261 Are signals at Pin’s 14 & 15 of U4201? Check R4201 Check C4381 Is U4201 pin 2 >4.5 VDC in Rx &