Figure 7-15. Synthesizer Block Diagram - Motorola HT Series Detailed Service Manual

Low Band, 800 MHz, PassPort & 900 MHz Theory of Operation: 900 MHz Synthesizer
Both the normal and adapt charge pumps get their supply from the capacitive multiplier which is
made up of CR201, CR202, C244, C245, C246, C247, R200, R218, C208, C243, R219, and R220.
Two 3.3 V square waves (180 degrees out of phase) are applied to R219 and R220. These square
waves switch alternate sets of diodes from CR201 and CR202, which in turn charge C244, C245,
C246, and C247 in a bucket brigade fashion. The resulting output voltage that is applied to pin 47 of
U201 is typically 12.8 V and allows the steering line voltage (VCO control voltage) to reach 11 V.
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
12.8V
Voltage
Multiplier
7
DATA
8
CLK
9
CEX
10
MODIN
13,30
V , DC5V
CC U251
V , 3.3V
Low Voltage
DD
Fractional-N
23
XTAL1
Synthesizer
24
XTAL2
25
WARP
32
PREIN
47
VCP
VMULT2 VMULT1
14
3.3Vp-p
3.3Vp-p

Figure 7-15. Synthesizer Block Diagram

4
LOCK
19
FREFOUT
6,22,23,24
GND
43
IOUT
45
IADAPT
41
MODOUT
3
AUX4
2
AUX3
28
SFOUT
40
BIAS1
39
BIAS2
AUX1
15 48
Transistors
5V
Prescaler In
LOCK (U409 Pin 56)
FREF (U201 Pin 21 & U404 Pin 34)
Steering
2-Pole
Line
Loop Filter
11.0V
Dual
Transistors Voltage
Controlled
Filtered 5V
Oscillator
Dual
R405
7-25
LO RF
Injection
TX RF
Injection
(First Stage of PA)