AKD4527B Datasheet, PDF (3/40 Pages) Asahi Kasei Microsystems – EVALUATION BOARD REV.D FOR AK4527B

ASAHI KASEI
[AKD4527B Rev.D]
3) Frequency response of LPF
1st-order RC LPF is implemented on board to attenuate the noise around the internal sampling frequency of
ADC (64fs=3.072MHz@fs=48kHz)
Frequency response of 1st-order LPF
| Amplitude |² = 1/{1+(f/fc)²}; fc=1/2πRC=169.3kHz@R=470,C=2000p
(1nF capacitance prior to ADC is doubled because of full-differential input.)
fin
20kHz
40kHz
Frequency Response -0.060dB -0.236dB
n Consideration for analog output circuit
3.0Vpp
AK4527
ROUT1 28
LOUT1 27 ^{Same circuit}
22u
10k
ROUT2 26 ^{Same circuit}
LOUT2 25 ^{Same circuit}
ROUT3 24 ^{Same circuit}
LOUT3 23 ^{Same circuit}
NJM5532
+
-
4.7k
4.7k
220
330p
6.0Vpp
Signal
1) Frequency response of HPF
The HPF is implemented on board to cancel the DC offset of analog output of AK4527B.
Frequency response of 1st-order HPF
| Amplitude |² = 1/{1+(fc/f)²}; fc=1/2πRC=0.7Hz@R=10k,C=22u
fin
20Hz
Frequency Response -0.006dB
2) Gain, S/N and frequency response of op-amp circuit
1st-order filter with non-inverting amp is implemented on board to double the analog output level and attenuate
out-of-band noise.
a) Gain
The gain is
1+4.7k/4.7k = +6.00dB.
Therefore the output level of this board is
0.51dBV(=3.0Vpp) + 6.00dB
= 6.51dBV = 6.0Vpp = 2.12Vrms.
b) S/N (Theory: BW=20k+A)
The output noise level of non-inverting amp
-110.36dBV = -116.87dB (0dB=6.51dBV)
S/N of DAC is
106.0dB (measurement)
Therefore total S/N of op-amp circuit and DAC is
105.66dB (measurement: 105.5dB).
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