AK2347B Datasheet, PDF (4/34 Pages) Asahi Kasei Microsystems – Two-way Radio Audio & Sub-Audio Processor

ASAHI KASEI
[AK2347B]
Block
TXA1
VR1
(HPF)
Compressor
Pre-emphasis
TX/RX_HPF
Scrambler/
Descrambler
TXA2
Adder
Limiter
VR2
Splatter
SMF
RXA1
VR3
RXLPF
De-emphasis
Expander
VR4
MS1419-E-00
5. Block Functions
Function
Operational amplifier for gain adjustment of transmit audio signal and for the filter for
preventing aliasing noise of the SCF circuit in the subsequent stage. Use external
resistors and capacitors to set the gain to 30dB or less and the cut-off frequency to
around 10kHz.
This circuit controls the volume for adjusting the input level of transmit audio signal.
Setting registers: VR12 to VR10, adjustment range: -6.0dB to +4.5dB in 1.5dB steps
This circuit compresses the amplitude of transmit audio signal by 1/2 in dB scale.
Cross-point: -10dBx. This circuit is turned on and off by the TC register.
This circuit emphasizes the high-frequency component of transmit audio signal to
improve the S/N ratio of the modulation signal.
High-pass filter to eliminate low-frequency components lower than 250Hz which are
included in transmit and receive audio signals. This circuit is turned on and off by the
HPF register.
This circuit inverts the spectrum distribution of transmit and receive audio signals with
respect to the carrier frequency.
The carrier frequency is 3.388kHz or 3.290kHz.
The Scrambler/Descrambler or emphasis circuit can be selected using the EM and
PCONT registers. These circuits cannot be used at the same time.
Operational amplifier for gain adjustment of external tone signal. Use external resistors
and capacitors to set the gain to 0dB or less and the cut-off frequency to around 10kHz.
This circuit adds together the audio signal and external tone input signal. This circuit is
controlled by the TXSW2 and TXSW1 register.
Amplitude limiting circuit to suppress frequency deviation in the modulation signal.
The limit level can be adjusted by applying a DC voltage to the LIMLV pin. When the
pin is left open, the level predetermined within the device is output. This circuit is turned
on and off by the LMT register.
This circuit controls the volume for adjusting the output level on the MOD pin. Setting
registers: VR25 to VR20, adjustment range: -3.2dB to +3.0dB in 0.2dB steps. For
coarse adjustment, switching between -6.4dB and 0dB is possible.
Low-pass filter to eliminate high-frequency components higher than 3kHz which are
included in the limiter output signal. The cut-off frequency can be adjusted with the SPL
register.
Smoothing filter to eliminate the high-frequency and clock components generated in the
SCF circuit.
Operational amplifier for gain adjustment of the receive demodulation signal and for the
filter for preventing aliasing noise in the SCF circuit in the subsequent stage. Use
external resistors and capacitors to set the gain to 20dB or less and the cut-off frequency
to around 40kHz.
This circuit controls the volume for adjusting the input level of the receive demodulation
signal.
Setting registers: VR33 to VR30, adjustment range: -4.0dB to +3.5dB in 0.5dB steps
Low-pass filter to eliminate high-frequency components higher than 3kHz which are
included in the receive demodulation signal.
This circuit restores the original state of the signal of which high-frequency component
has been emphasized by the Pre-emphasis.
This circuit expands the signal compressed twice by the Compressor in dB scale to
restore the original signal state.
Cross-point: -10dBx. The Expander is turned on and off with the TC register.
This circuit controls the volume for adjusting the RX output level.
Setting registers: VR45 to VR40 Adjustment range: -18.0dB, -4.5dB to +4.5dB in
0.25dB steps
2012/05
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