ASAHI KASEI
[AK2346B]
5. Circuit Configuration
Block
TXA1
VR1
(HPF)
Compressor
Pre-emphasis
TX/RXHPF
Scrambler/
Descrambler
Description
The operational amplifier for transmit audio gain adjustment and for the filter to eliminate
aliasing noise by the SCF(switched capacitor filter) in the following stage. Please select
an external resistor and capacitor to set the gain less than 30dB and the cut-off frequency
to about 10kHz.
Digitally controlled amplifier (volume) for transmit audio signal level which is adjustable in
1.5dB steps over a –6.0dB to +4.5dB range by setting VR12 to VR10 register.
The circuit to compress transmits audio signal level by 1/2 in dB scale.
Standard cross-point is –10dBx. TC register sets OFF/ON to the circuit.
The circuit to emphasis the high-frequency component of transmit audio signal to improve
S/N ratio of the modulation signal.
The High-pass filter to eliminate the low-frequency component less than 250Hz for
transmit and receive audio signal.
Scramble/De-scramble circuit to inverse transmit and receive audio spectrum by
3.388kHz carrier signal.
EM and PCONT register can set scramble/De-scramble or Emphasis circuit. Both circuits
do not use simultaneously.
An amplitude limiting circuit to suppress the frequency deviation of the modulation signal.
The limitation level can be adjusted by applying a DC voltage to the LIMLV pin. If the
LIMLV pin is open, the limitation level is applied to a predetermined level.
The circuit to eliminate the high frequency component higher than 3kHz included in the
limiter output signal or the MSK modulator signal. The cut-off frequency can be selected
by SPL register.
Digitally controlled amplifier (volume) for MOD output level which is adjustable in 0.2dB
steps over a –3.2dB to +3.0dB range by setting VR25 to VR20 register. VR25 is a –6/0dB
coarse bit.
The smoothing filter to eliminate the high frequency and clock component caused in SCF
circuits.
The operational amplifier for receives audio gain adjustment and for the filter to eliminate
aliasing noise by the SCF in the following stage. Please select an external resistor and
capacitor to set the gain less than 20dB and the cut-off frequency to about 40kHz.
Digitally controlled amplifier (volume) for receive audio signal level which is adjustable in
0.5dB steps over a –4.0dB to +3.5dB range by setting VR33 to VR30 register.
The Low-pass filter to eliminate the high frequency component higher than 3kHz for
receive audio signal.
The circuit to de-emphasis the emphasized signal by pre-emphasis circuit.
The circuit to expand the receive audio signal level to double in dB scale compressed by
compressor
Standard cross-point is –10dBx. TC register sets OFF/ON to the circuit.
Digitally controlled amplifier (volume) for EXPOUT output level which is adjustable in
1.5dB, steps over a –18dB and –4.5dB to +4.5dB range by setting VR42 to VR40 register.
The operational amplifier used on smoothing filter to eliminate clock component included
in EXPOUT output signal. Please set the gain to 0dB and the cut-off frequency to about
20kHz by external resistor and capacitor.
The circuit to generate a MSK signal according to the received digital data from TDATA
pin.
The Band-pass filter to eliminate the low and high frequency component for received MSK
signal.
The circuit to reproduce the 1200/2400bps receive clock and data from MSK signal at
RXIN pin.
Limiter
Splatter
VR2
SMF
RXA1
VR3
RXLPF
De-emphasis
Expander
VR4
RXA2
MSK Modulator
MSK BPF
MSK Demodulator
MS1409-E-00
-4-
2012/05
AKM [ ASAHI KASEI MICROSYSTEMS ]
