AK5394A Datasheet, PDF (22/24 Pages) Asahi Kasei Microsystems – Super High Performance 192kHz 24-Bit ADC

ASAHI KASEI
[AK5394A]
6. Noise floor of AK5394A
The AK5394A has a sprious noise of about −135dBFS on the noise floor of Lch output at no signal input. When this noise
causes a trouble in system, it can be removed by adding a minute offset to the analog inputs of both channels externally
using a circuit as Figure 13. The relationship between the frequency range (f_T) of the sprious noise to be removed and the
adding offset voltage (V_of) is f_T [kHz] = 20 x V_of [mV] − 20. The example is shown in Table 10.
Sprious noise Frequency
Offset Voltage
0 ∼ 20kHz
+2mV
0 ∼ 40kHz
+3mV
0 ∼ 80kHz
+5mV
Table 10. Sprious noise Frequency vs. Offset voltage
A resistor, R in Figure 13 should be 8Ω to add an offset of 2mV to the analog inputs. The relationship between R and V_of
is shown by the following equation.
V_of
= ^R × 5[V ]
20k + R
An offset voltage of the op-amps should be considered in the actual circuit. For example, when removing the sprious noise
of 20kHz or less, the adding offset voltage should be 2+2=4mV if the op-amp has an offset of +/−2mV. In this case, the
dynamic range of the ADC output decreases 4mV.
5V
10k
Bias+
620
1n
Vin+ ^68µ 3.3k
91
-
+
Bias+
NJM5534
XLR
R
+
10k
10µ
Bias-
0.1µ
620
1n
68µ _3.3k
-
91
Vin-
+
NJM5534
Bias-
Figure 13. Removing the sprious noise circuit
AK5394A AIN+
2.2n
AK5394A AIN-
MS0137-E-01
- 22 -
2002/07