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| OPA1632 Datasheet, PDF (14/30 Pages) Texas Instruments – High-Perfomance, Fully-Differential AUDIO OP AMP | |||
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OPA1632
SBOS286C â DECEMBER 2003 â REVISED OCTOBER 2015
www.ti.com
The VCOM reference voltage output on the PCM1804 ADC provides the proper input common-mode reference
voltage (2.5 V). This VCOM voltage is buffered with op amp A2 and drives the output common-mode voltage pin of
the OPA1632. This biases the average output voltage of the OPA1632 to 2.5 V.
The signal gain of the circuit is generally set to approximately 0.25 to be compatible with commonly-used audio
line levels. Gain can be adjusted, if necessary, by changing the values of R1 and R2. The feedback resistor
values (R3 and R4) should be kept relatively low, as indicated, for best noise performance.
R5, R6, and C3 provide an input filter and charge glitch reservoir for the ADC. The values shown are generally
satisfactory. Some adjustment of the values may help optimize performance with different ADCs.
It is important to maintain accurate resistor matching on R1/R2 and R3/R4 to achieve good differential signal
balance. Use 1% resistors for highest performance. When connected for single-ended inputs (inverting input
grounded, as shown in Figure 14), the source impedance must be low. Differential input sources must have well-
balanced or low source impedance.
Capacitors C1, C2, and C3 should be chosen carefully for good distortion performance. Polystyrene,
polypropylene, NPO ceramic, and mica types are generally excellent. Polyester and high-K ceramic types such
as Z5U can create distortion.
8.2.3 Application Curves
0.1
Gain = +1
RF = 348W
f = 1kHz
0.01 Differential I/O
0.001
0.0001
RL = 600W
RL = 2kW
0.00001
0.01
0.1
1
10
100
Differential Output Voltage (VRMS)
Figure 15. THD + Noise vs Output Voltage
0.01
0.001
RL = 600W
0.0001 Gain = +1
RF = 348W
f = 1kHz
Single-Ended Input
Differential Output
0.00001
0.01
0.1
1
RL = 2kW
10
100
Differential Output Voltage (VRMS)
Figure 16. THD + Noise vs Output Voltage
14
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