Motorola Astro Digital Mobile Radio Xtl5000 Detailled 6881096c74 B Manual

6881096C74-BMay 25, 2005
Theory of Operation: Frequency Generation Unit (FGU) 3-55
3.7.3.1  Reference Oscillator
The radios frequency stability and accuracy is derived from the 16.8 MHz reference oscillator 
(Y5750). The 16.8 MHz reference oscillator circuitry provides a 16.8 MHz reference to the LV Frac-N 
(U5752), receiver back-end IC (U5002), and the controller section of the XTL 5000 radio. The 
reference oscillator circuitry consists of the reference oscillator Y5750 and the inverter/buffer...

May 25, 20056881096C74-B
3-56Theory of Operation: Frequency Generation Unit (FGU)
3.7.3.4  Superfilter
The superfilter is an active filter that provides a low-noise supply for the VCOs, receiver and 
transmitter injection amplifiers. Regulator U0950, located in the controller section, supplies 9.3 Vdc 
to the FGU section thru the filtering network consisting of L5750, C5751, C5753, and C5755. This 
voltage is applied to pin 30 (SFIN) of U5752 and the emitter of Q5752. The output is a superfiltered 
8.2...

6881096C74-BMay 25, 2005
Theory of Operation: Frequency Generation Unit (FGU) 3-57
3.7.3.9  Transmitter Injection
The transmit (TX) injection string consists of three amplifier stages (Q5828, Q5829, and Q5501) 
whose main purpose is to maintain a constant output to drive the RF power amplifier chain and 
supply the TX feedback signal to the FGU synthesizer loop. The first two stages are powered by the 
superfiltered 8.2 Vdc, which is decreased by 0.7 Vdc via the dual diode D5833, resulting in a 7.5 Vdc...

May 25, 20056881096C74-B
3-58Theory of Operation: Frequency Generation Unit (FGU)
3.7.3.13 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.
3.7.4 700–800 MHz Band
The FGU (Figure 3-41) provides the XTL 5000 radio...

6881096C74-BMay 25, 2005
Theory of Operation: Frequency Generation Unit (FGU) 3-59
3.7.4.1  Reference Oscillator
The radios frequency stability and accuracy is derived from the 16.8 MHz reference oscillator 
(Y6750). The 16.8 MHz reference oscillator circuitry provides a 16.8 MHz reference to the LV Frac-N 
(U6751), receiver back-end IC (U6000), and the controller section of the XTL 5000 radio. The 
reference oscillator circuitry consists of the reference oscillator Y6750 and the inverter/buffer...

May 25, 20056881096C74-B
3-60Theory of Operation: Frequency Generation Unit (FGU)
3.7.4.4  Superfilter
The superfilter is an active filter that provides a low-noise supply for the VCOs, receiver and 
transmitter injection amplifiers. Regulator U0950, located in the controller section, supplies 9.3 Vdc 
to the FGU section thru the filtering network consisting of L6755, C6806, C6807, and C6818. This 
voltage is applied to pin 30 (SFIN) of U6751 and the emitter of Q6759. The output is a superfiltered 
8.2...

6881096C74-BMay 25, 2005
Theory of Operation: Frequency Generation Unit (FGU) 3-61
3.7.4.9  Transmitter Injection
The transmit (TX) injection string consists of three amplifier stages (Q6764, Q6765, and Q6766) 
whose main purpose is to maintain a constant output to drive the RF power amplifier and supply the 
TX feedback signal to the FGU synthesizer loop. The first two stages are powered by the 
superfiltered 8.2 Vdc, which is decreased by 0.7 Vdc via the dual diode D6750, resulting in a 7.5 Vdc...

May 25, 20056881096C74-B
3-62Theory of Operation: Controller Section
3.7.4.12 Receiver VCOs
Receiver first local-oscillator frequencies are generated from two VCOs in U6755. U6755 is not 
serviceable and should be replaced if determined to be non-functional. For receiver frequencies in 
the range of 764 to 776 MHz, high-side, first local-oscillator injection of 837.35 to 849.35 MHz (Fc + 
73.35 MHz) is generated when Aux3 (pin 2) of U6751 is active high (3.0 Vdc). This 3.0 volts is 
applied to transistor...

6881096C74-BMay 25, 2005
Theory of Operation: Controller Section3-63
Figure 3-43.  XTL 5000 Controller Section
The controller consists of digital logic comprised of a microprocessor (the Patriot IC, U100) and 
memory consisting of a 512K x 16 SRAM (U103) and a 4M x 16 FLASH ROM (U102). The 
microprocessor is a dual-core processor that contains a DSP56600 core and an MCORE 
microcontroller with custom peripherals. The term, MCU, refers to the MCORE controller section of 
the Patriot IC. The FLASH ROM...

May 25, 20056881096C74-B
3-64Theory of Operation: Controller Section
In receive mode, the ABACUS III IC provides data samples directly to the DSP for processing. In 
transmit mode, the DAC provides a serial D/A converter. The data generated by the DSP is filtered 
and reconstructed as an analog signal to present a modulation signal to the VCO (voltage-controlled 
oscillator) at the LV Frac-N synthesizer. Both the transmit and receive digital data paths between the 
DSP and the CODEC are through the...