AKD4528 Datasheet, PDF (2/38 Pages) Asahi Kasei Microsystems – EVALUATION BOARD FOR AK4528 REV.C

ASAHI KASEI
[AKD4528]
1. Analog Input Buffer Circuit
The ADC inputs are full differential and the input resistance is 27kΩ (typ. @fs=44.1kHz). The input signal range scales
with the VREF voltage and nominally 0.56 x VREF Vpp. It is recommended that the input DC bias voltage is 2.9V(The
bias is a voltage divided by resistors (3.3k and 4.7k) from VA in figure 2. The ADC output data format is 2’s complement.
The output code is 7FFFFFH(@24bit) for input above a positive full scale and 800000H(@24bit) for input below a
negative fill scale. The ideal code is 000000H(@24bit) with no input signal. The DC offset including ADC own DC offset
removed by the internal HPF (fc=0.9Hz@fs=44.1kHz).
The AK4528 samples the analog inputs at 64fs. The digital filter rejects noise above the stopband except for multiples of
64fs. A simple RC filter may be used to attenuate any noise around 64fs though most audio signals do not have significant
energy at 64fs. Figure 2 is an example of differential input circuit.
2.8Vpp
4.7k
AK4528
1.5nF ³³⁰
AINR+ 2
-
+
330 NJM5532
AINR- 3
AINL+ 4
2.8Vpp
AINL- 5
Same circuit
5.96Vpp
4.7k
Vop+
4.7k
-
+
Vop-
10k 22u
Signal
VA
Vop+/-=+/-15V
VA=5V
3.3k
BIAS
4.7k
0.1u
+
10u
Input RC filter response : fc = 160kHz, g = -0.07dB at 20kHz, -0.26dB at 40kHz.
Figure 2. Differential Input Buffer Example
2.Analog Output Buffer Circuit
The 2nd-order LPF (fc=93.2kHz, Q=0.712) which adds differential output of AK4528 is implemented on the board.
When the further attenuation of the out-band noise is needed, some additional LPF is required. NJM5532D is used for
op-amp. Analog signal is output through BNC connectors (AOUTL, AOUTR) on board, and the output level of AK4528is
about 5.4Vp-p.
AOUT-
4.7k
4.7k
200
470p
AOUT+
3300p
4.7k
4.7k
+Vop
200
-
+
470p -Vop
Analog
Out
fc=93.2kHz, Q=0.712, g=-0.1dB at 40kHz
Figure 3. External 2nd order LPF Example (using dual supply op-amp)
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