June 15, 2005
6815854H01-A
3-58
Theory of Operation:
Frequency Generation Unit (FGU)
3.13.3.13 Prescaler Feedback
RF feedback for the synthesizer loop is provided by prescaler amplifier Q5755. Feedback from both
the transmitter and receiver injection strings are coupled to this amplifier through capacitors C5863
and C5957. The output of Q5755 is coupled to U5752 at pin 32 (PREIN), which is the prescaler input
for the synthesizer.
3.13.4 700–800 MHz Band
The FGU (
) provides the XTL 1500 radio with a 16.8 MHz reference frequency, receiver
1st local oscillator, and a modulated transmitter RF carrier that is further amplified by the power
amplifier section of the radio.
The FGU consists of the following:
• Reference oscillator (Y6750)
• Low-voltage Fractional-N (LV Frac-N) synthesizer (U6751)
• Two receiver voltage-controlled oscillators (VCOs) contained in U6755
• Two transmitter VCOs contained in U6754
• Two receiver LO amplifiers (Q6762 and Q6763)
• Three transmitter injection amplifiers (Q6764, Q6765 and Q6766)
Figure 3-40. Frequency Generation Unit Block Diagram (700–800 MHz)
Bias 1
3.0V
3.0V
3.0V
3.0V
8.2V
8.2V
8.2V
Q6753
Q6755
Q6756
Q6760
Lock Detect
to Controller
Prescaler Input
Q6761
RF
Feedback
RX
INJECTION
TX
INJECTION
RX
Injection
TX
Injection
Keyed
9.1V
U6754
U6755
8.2V
C6783
LOOP
FILTER
Bias 2
9.3V
9.3V
SFIN
SFBASE
SFOUT
Lock
PREIN
AUX4
AUX3
Mod Out
IADAPT
IOUT
AUX2
AUX1
VMULT4
VMULT3
5.0V
16.8MHz Reference
to Controller and
Receiver Back End
VOLTAGE
MULTIPLIER
D6751 and
D6752
16.8MHz OSC
8.2V
Super Filter
Q6759
8.2V SW
8.2V SW
8.2V SW
8.2V SW
U6752
U6751
3.0V
Regulator
U6750
PHASE
DETECTOR BIAS
Q6757 RX and
Q6758 TX
CLOCK
SYN_SEL
DATA
MOD_IN
From
Controller
MAEPF-27804-O
Содержание XTL 1500
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