Circuit Operation Of Portable Handset - Panasonic KX-F900 Service Manual

Kx:F900 I
13-7. CIRCUIT OPERATION OF PORTABLE HANDSET
(1) Power Supply Ciurcuit
As indicated in Fig.40, voltage is supplied separately to each block. In order to ensure that the RF block in
particular has a stable fixed-voltage power supply, the RF block is equipped with a dedicated stabilized power
supply. In the standby mode, pin 58 drops at set intervals from high to low level, resulting in an intermittent recep-
tion signal. In the talk mode, pins 59 and 58are low level and power is supplied to all the circuitry.
Circuit Diagram
T
1
RX POWER I
sw 1
Q203 R_
PU RX POWER
TX POWER I
205
SPK AMP SW
_ )_ CPU TX POWER
> RINGER(Q212,Q213)
• CPU (IC201)
• DATA AMP(Q215,Q214)
IF Part (RF BLOCK )
• RF BLOCK
• COMPANDER (IC202)
(IC203)
• RF BLOCK, MICAMP(Q208)
> SPK AMP(Q210,Q211)
(2) Data Reception Circuit
The wave detection signal from the RF block has high frequency elements eliminated by a CR filter consisting of
R258 and C244. Then it is amplified by Q215 and, once again, high frequency elements are eliminated by R255
and C243. After this, the signal is amplified by Q214 and input to pin 50 of the CPU. (The cutoff frequency is 500
Hz.) The data output waveform is a block pulse. To inhibit block pulse noise, the gain of the amplifier is limited
and modulation is clipped at 3 kHz.
Circuit Diagram
- R_57
1._ _ iQ215_ from
RF BLOCK AF Output
- 180-