Motorola Gm328 Gm338 Gm398 Detailed 6804112j18 E Manual

							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. 
						

							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. 
						

							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 
						

							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 
						

							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. 
						

							2-10Frequency Synthesis
THIS PAGE INTENTIONALLY LEFT BLANK 
						

							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? 
						

							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? 
						

							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 
						

							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 &