2-6
Frequency Synthesis
4.0
Frequency Synthesis
The frequency synthesizer subsystem consists of the reference oscillator (Y3261 or Y3262), the
Low Voltage Fractional-N synthesizer (LVFRAC-N, U3201), and the voltage-controlled oscillators
and buffer amplifiers (U3301, Q3301-2 and associated circuits).
4.1
Reference Oscillator
The reference oscillator (Y3262) contains a temperature compensated crystal oscillator with a
frequency of 16.8 MHz. An analog-to-digital (A/D) converter internal to U3201 (LVFRAC-N) and
controlled by the µP via serial interface (SRL) sets the voltage at the warp output of U3201 (pin 25)
to set the frequency of the oscillator. The output of the oscillator (U3262 pin 3) is applied to pin 23
(XTAL1) of U3201 via R3263 and C3235.
In applications were less frequency stability is required, the oscillator inside U3201 is used along
with an external crystal Y3261, varactor diode D3261, C3261, C3262 and R3262. In this case,
Y3262, R3263, C3235 and C3251 are not used. When Y3262 is used, Y3261, D3261, C3261,
C3262 and R3262 are not used, and C3263 is increased to 0.1 uF.
4.2
Fractional-N Synthesizer
The LVFRAC-N synthesizer IC (U3201) 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 balance attenuator to balance the high frequency analog modulation and low
frequency digital modulation, a 13 volt positive voltage multiplier, a serial interface for control, and
finally a super filter for the regulated 5 volts.
Figure 2-3 VHF Synthesizer Block Diagram
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 (U3211 PIN 1)
7
8
9
10
13, 30
23
24
25
32
47
VMULT2
VMULT1
BIAS1
SFOUT
AUX3
AUX4
IADAPT
IOUT
GND
FREFOUT
LOCK
4
19
6, 22, 33, 44
43
45
3
2
28
14
15
40
FILTERED 5V
STEERING
LOCK (U0101 PIN 56)
PRESCALER IN
FREF (U0221 PIN 34)
39
BIAS2
41
48
5, 20, 34, 36
+5V (U3211 PIN 1)
AUX1
VDD, DC5V
MODOUT
U3201
LOW VOLTAGE
FRACTIONAL-N
SYNTHESIZER
AUX2
TRB
TX RF INJECTION
(1ST STAGE OF PA)
LO RF INJECTION
VOLTAGE
CONTROLLED
OSCILLATOR
LINE
2-POLE
LOOP
FILTER
1
Summary of Contents for GM338
Page 1: ...GM328 GM338 GM398 Mobile Radios Detailed Service Manual 6804112J18 E December 2003 ...
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Page 7: ...GM328 GM338 GM398 Mobile Radios Service Maintainability Issue December 2003 ...
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Page 20: ...1 4 Radio Model Information THIS PAGE INTENTIONALLY LEFT BLANK ...
Page 32: ...2 12 Notes For All Schematics and Circuit Boards THIS PAGE INTENTIONALLY LEFT BLANK ...
Page 35: ...GM328 GM338 GM398 Mobile Radios Controlhead Service Information Issue December 2003 ...
Page 42: ...1 4 GM398 Model GCN6115_ THIS PAGE INTENTIONALLY LEFT BLANK ...
Page 56: ...2 14 Controlhead Model for GM398 THIS PAGE INTENTIONALLY LEFT BLANK ...
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Page 88: ...4 20 Controlhead GM398 PCB 8486178B03 Schematics THIS PAGE INTENTIONALLY LEFT BLANK ...
Page 89: ...GM328 GM338 GM398 Mobile Radios Controller Service Information Issue December 2003 ...
Page 114: ...2 2 Controller Troubleshooting Chart THIS PAGE INTENTIONALLY LEFT BLANK ...
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Page 141: ...GM328 GM338 GM398 Mobile Radios VHF 136 174MHz Service Information Issue December 2003 ...
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Page 187: ...GM328 GM338 GM398 Mobile Radios UHF 403 470MHz Service Information Issue December 2003 ...
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Page 411: ...GM338 Mobile Radios UHF1 40W Bipolar 403 470MHz Service Information Issue December 2003 ...
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Page 447: ...GM338 Mobile Radios UHF2 40W Bipolar 450 520MHz Service Information Issue December 2003 ...
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Page 483: ...GM338 Mobile Radio UHF B1 HIGH POWER LDMOS 403 470MHz Service Information Issue December 2003 ...
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