Motorola Astro Digitalport Saber Detailed 68p81076c10 A Manual

6-4
of U205 via bypass C213. The mixer’s LO port is matched to the radio’s 
PLL by a capacitive tap, C207 and C206. A balun transformer (T202) is 
used to couple the RF signal into the mixer. The primary of T202 is 
matched to the preceding stage by capacitor C223, with C227 
providing a dc block to ground. The secondary of T202 provides a 
differential output, with a 180° phase differential being achieved by 
setting the secondary center tap to virtual ground using bypass 
capacitors C210, C211 and...

6-5
TransmitterThe 800MHz RF power amplifier (PA) is a 5-stage amplifier (U502). The 
RF power amplifier has a nominal input and output impedance of 50 
ohms. 
An RF input drive level of approximately +3dBm, supplied from the 
VCO buffer IC (U303), is applied to pin 1 of U502. The dc bias for the 
internal stages of U502 is applied to pins 2, 5, and 6 of the module. 
Pins 2 and 5 being switched through Q502 and pin 6 being 
unswitched B+ to the final amplifier stage. Power control is achieved 
through the...

6-6
Notes 

7-1
VOCON Board 
Detailed Theory of Operation
7
IntroductionThis section of the manual provides a detailed circuit description of an 
ASTRO Digital SABER VOCON (Vocoder/Controller) Board. When 
reading the theory of operation, refer to your appropriate schematic 
and component location diagrams located in the back section of this 
manual. This detailed theory of operation will help isolate the 
problem to a particular component. However, first use the ASTRO 
Digital SABER Portable Radios Basic Service...

7-2
Controller SectionRefer to Figure 4 and your specific schematic diagram.
The controller section of the VOCON board consists entirely of digital 
logic comprised of a microcontrol unit (MCU-U204), a custom support 
logic IC (SLIC-U206), and memory consisting of: SRAM (U202), 
EEPROM (U201), and FLASH memory (U205, U210).
The MCU (U204) memory system is comprised of a 32k x 8 SRAM 
(U202), 32k x 8 EEPROM (U201), and 512k x 8 FLASH ROM 
(U205,U210). The MCU also contains 1024 bytes of internal SRAM and...

7-3
The controller performs the programming of all peripheral ICs. This is 
done through a serial peripheral interface (SPI) bus. ICs programmed 
through this bus include the synthesizer, DAIC, reference oscillator, 
display, and ADSIC. On secure-equipped model, the encryption board 
is also controlled through the SPI bus.
In addition to the SPI bus, the controller also maintains two 
asynchronous serial busses; the SB9600 bus and an RS232 serial bus. 
The SB9600 bus is for interfacing the controller...

7-4
In the transmit mode, the ADSIC (U406) provides a serial digital-to-
analog (D/A) converter. The data generated by the DSP is filtered and 
reconstructed as an analog signal to present to the VCO as a 
modulation signal. Both the transmit and receive data paths between 
the DSP and ADSIC are through the DSP SSI port. 
The only analog device in the vocoder section is the audio PA (U401). 
This IC is an audio amplifier for the microphone analog input and 
speaker analog output. The audio PA allows...

7-5
Switched RegulatorAll of the digital circuitry on the VOCON is supplied 5 volt regulated 
dc by a switched mode regulator (refer to  Figure 3 on page 5 of Chapter 
4). The fundamental parts of the regulator are U409, L402, C470, 
CR403, C463, and U407. Module U409 is a pulse width modulating 
(PWM) switched regulator controller. Coil L402 is an energy storage 
element, C470 is an output ripple filter, and CR403 is a Schottky diode 
switch. Capacitor C463 is added for UNSW_B+ ripple filter and is...

7-6
RX Signal PathThe vocoder processes all received signals digitally. This requires a 
unique back end from a standard analog radio. This unique 
functionality is provided by the ABACUS IC with the ADSIC (U406) 
acting as the interface to the DSP. The ABACUS IC located on the 
transceiver board provides a digital back end for the receiver section. 
It provides a digital output of I (In phase) and Q (Quadrature) data 
words which represent the IF (Intermediate Frequency) signal at the 
receiver back end...

7-7
DIN and DIN* are the data lines in which the I and Q data words are 
transferred from the ABACUS. These signals make up a deferentially 
encoded current loop. Instead of sending TTL type voltage signals, the 
data is transferred by flowing current one way or the other through the 
loop. This helps reduce internally generated spurious emissions on the 
transceiver board. The ADSIC contains an internal current loop 
decoder which translates these signals back to TTL logic and stores the 
data in...