CL-D26X
CIRCUIT DESCRIPTION
Introduction
This new cordless phone features 10 channel access and speaker phone system. Digital security code is utilized for command
control. The digital security code is randomly generated with combination over 65000 which will forbid invalid access and
misconnection. The phone will utilize the 10 channels as far as possible. The carrier detect circuit in the RF receiver system
will automatically scan for vacant channel before communication is established. Any occupied channel or noisy channel will
be automatically bypassed.
BASE UNIT
Speakerphone
U9
VccSwitch CircuitU8D
Charge
CurrentU10
ControlMICU8C
Charge
DetectionU7ATO MCU
SPEAKER
U7B
HTO+U7D+
U9
+EEPROM
DTMF
HTO-
Side ToneU8B
Cancellation
U2 KEYPAD
U7C
MCU
U8A
MCU Tx DATA
U9
6MHz
+XtalQ1Q2,Q3
VCO
Transmit Audio
Tip
ReceivedRF Transmitter
RingDataDual
HoldProtectionPLLDetection
Detect
10.24MHzDuplexer
Ring
OSCVCO
2nd mixer1st mixer
FM
Detect
Recovered
AudioU1Q8
RF Front
End
455kHz10.7MHzRF Receiver
BPF2BPF1
Figure 21 BASE UNIT BLOCK DIAGRAM
1. Receiver Portion
Tuner PartIF part
The receiver part of the cordless telephone uses the1st IF for CH1 signal which is the difference (49.670 -
superheterodyne system.38.975 = 10.695 MHz) is fed to 2nd MIXER through
The selectivity and sensitivity are improved by carrying10.695 MHz 1st IF filter CF2. The 2nd IF signal is obtained
out the 2 times heterodyne detection.by mixer the 10.695MHz IF signal with 2nd local signal
10.240 MHz. The 2nd IF, 455 kHz, is then fed to the IF
In order to tune 2 times, there are 2 local oscillators and
amplifier via the 455 kHz filter CF1. The 455 kHz signal is
the 1st local oscillator is variable and the 2nd oscillator is
then demodulated via quadrature demodulation system
fixed. The block diagram is shown below.
formed by the U1 and quadrature coil T6.
The quadrature FM detector is one of the several popular
RF1st1st IF 2nd2nd IF
FM detector such as peak differential, PLL PULSE COUNT
Amp.Mixer10.695 MHz Mixer455 kHzetc. The quadrature detector is formed by U1 with T6 in
the baseunit and U1 with T2 in the handset.
MultiplierDelay vs Frequency
Voice180!
1st Local2nd Local OSCDetect Out
LC VCO10.240 MHzData
90!
An incoming RF signal from the Handset (49.670 - 49.990
Delay
MHz) which is fed to ANTENNA. The RF signal is then~~0!
passed through the duplexer. The receiving frequency455 kHz
signal is passed to the RF front end which is comprised ofThe recovered signal is splitted into voice audio and FSK
data detection. The audio signal through low pass filter
low noise FET Q6 and the tank coil T4. The amplified
and expander is amplified by operational amplifier in the
signal is supplied to 1st MIXER of the RF combo IC U1.
RF system IC and audio amplifier. The detected FSK
The received RF signal then mixed with Rx LOCAL VCO
signal from compander is fed to microcomputer U2
signal (38.975 - 39.295 MHz) to form the 1st intermediate
through comparator.
frequency.
N 21 N |
ACEC
