Motorola Professional GP680 Service Information - Page 15

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Motorola Professional GP680 Service Information
Frequency Generation Circuitry
In achieving fast locking for the synthesizer, an internal adapt charge pump provides higher current
at pin 45 of U201 to put synthesizer within the lock range. The required frequency is then locked by
normal mode charge pump at pin 43 .
Both the normal and adapt charge pumps get their supply from the capacitive voltage multiplier
which is made up of C258, C259, C228, triple diode CR201 and level shifters U210 and U211. Two
3.3V square waves (180 deg out of phase) are first shifted to 5V, then along with regulated 5V , put
through arrays of diodes and capacitors to build up 13.3V at pin 47 of U201.
DATA (U409 PIN 100)
CLOCK (U409 PIN 1)
CSX (U409 PIN 2)
MOD IN (U404 PIN 40)
+5V (U247 PIN 4)
5, 20, 34, 36
(U248 PIN 5)
REFERENCE
OSCILLATOR
VOLTAGE
MULTIPLIER
7
DATA
8
CLK
9
CEX
U251
LOW VOLTAGE
10
MODIN
FRACTIONAL-N
13, 30
SYNTHESIZER
V
, DC5V
CC
V
, 3.3V
DD
23
XTAL1
24
XTAL2
25
WARP
32
PREIN
47
VCP
VMULT2
VMULT1
14
15
PRESCALER IN
Figure 2-4 Synthesizer Block Diagram
4
LOCK
19
FREFOUT
6, 22, 23, 24
GND
43
IOUT
45
IADAPT
41
MODOUT
3
AUX4
DUAL
TRANSIS
2
AUX3
TORS
FILTERED 5V
28
SFOUT
BIAS1
40
BIAS2
AUX1
39
48
DUAL
TRANSISTORS
5V
LOCK (U409 PIN 56)
FREF (U201 PIN 21 & U404 PIN 34)
STEERING
2-POLE
LINE
LOOP
FILTER
LO RF INJECTION
VOLTAGE
CONTROLLED
OSCILLATOR
TX RF INJECTION
(1ST STAGE OF PA)
R5
2-7