Digital & Audio Section, Detailed Circuit Description - Motorola MTP700 Detailed Service Manual

TRANSCEIVER 800 MHz
Transmit PLL
The TX VCO (Q463) is a discrete VCO that is controlled by the ESCORT IC U460. The
VCO produces the TX frequency signals in the frequency band 806-870MHz. A discrete
coil (resonator) Y460 and shunt capacitors are used as a tank circuit for VCO. The Col-
pitts Oscillator was adopted to ensure excellent performance in noise behavior and signal
level stability throughout the whole band. Cascade amplifier is used as buffer to minimize
the impact of load pull on the VCO frequency.
The synthesizer IC is the ESCORT IC employing NUD (near-unity-divider) technique to
provide fast lock-in to TX frequency using a high reference frequency. The Main synthe-
sizer is used as reference frequency source. The signal frequency of the Main VCO is
divided by 36/32 (NUD) and compared with the TX VCO frequency in the fast phase com-
parator of the ESCORT. The comparator output signals IUP and IDOWN are then control-
ling the current mirror Q460 to supply the right tuning voltage to tuning diode D460 via
loop filter R464, C472 and C473. ESCORT IC is controlled by RedCap2 via SPIA_CLK,
SPIA_MOSI and SPIA_CS1_ESCORT.
Digital & Audio Section, Detailed Circuit Description
See Figure 4.2-9
INT_SPKR
EXT_SPKR
INT_EAR
Vibrator
Side Data
EXT_MIC
SIDE_SWB+
On/Off
Vol knob
MTP700 Portable Radio / Detailed Service Manual
RF Section
Audio
PA
24-pin
Connector
REDCAP2
REDCAP2
Figure 4.2-9 Digital Section - Detailed Circuit Diagram
TETRA
TXE
BBP
SPIA
REDCAP2
SIDE_OPT_SEL3
(from 24-pin connector)
Radio Off
SPIB
GCAP3
Reset
Buffer
BOT_SWB+
ON3
Headset/Keyfail
INT_MIC
SIDE_OPT_SEL1
(from 24-pin connector)
SIDE_OPT_SEL2
(from 24-pin connector)
Display
40-pin
Connector
Keypad
FLASH 4M x 16 bit
SRAM 512k x 16 bit
OPT SEL
JTAG
16-pin
Connector
USB/RS232
4.2 - 19