AK2346A Datasheet, PDF (4/37 Pages) Asahi Kasei Microsystems – Two-way Radio Audio Processor

ASAHI KASEI
[AK2346A]
Block
TXA1
VR1
(HPF)
Compressor
Pre-emphasis
TX/RXHPF
Scrambler/
Descrambler
Adder1/2
Limiter
DAC
VR2
Splatter
SMF
RXA1
VR3
RXLPF
De-emphasis
Expander
VR4
TXA2
MS1289-E-02
5. Circuit Configuration
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 –18.0dB to +4.5dB range by setting VR13 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.
This circuit is turned on and off by HPFSW register.
Scramble/De-scramble circuit to inverse transmit and receive audio spectrum by 2.844 to
3.491kHz carrier signal.
EM and PCONT register can set scramble/de-scramble or emphasis circuit. Both circuits
can not be used simultaneously.
The circuit to add audio signal and external tone signal.
TXINSW,TXSW2,1,0 registers are used to set this block.
An amplitude limiting circuit to suppress the frequency deviation of the modulation signal.
The limitation level can be adjusted by internal DAC.
Digitally controlled amplifier (volume) for the limitation level of the limiter circuit which is
adjustable in 0.5dB steps over a -17.6dB to -2.1dB range by setting LIMLV3 toLIMLV0
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
–6.4/0dB coarse bit.
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.
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 Expander output level which is adjustable in
0.25dB, steps over a –18dB and –4.5dB to +4.5dB range by setting VR42 to VR40
register.
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.
2012/06
-4-