Datasheet


SBAS342B − DECEMBER 2004 − REVISED APRIL 2006
www.ti.com
17
For single-ended or unbalanced inputs, the input buffer
circuit shown in Figure 12 provides the conversion to a
differential signal required for the PCM4201 analog inputs.
The buffer circuit may be configured for the appropriate
gain/attenuation using resistors R1 and R2. Capacitor C1
is chosen to provide the low-pass corner frequency.
Additional low-pass filtering is provided by the RC network
at the output of the buffer.
A differential input buffer circuit is shown in Figure 13. Like
the unbalanced circuit, the differential buffer
gain/attenuation may be set by using the R1/R2 and R3/R4
resistor pairs. The resulting gain or attenuation must be the
same for both pairs. Filtering is provided by the feedback
capacitors and the capacitors at the buffer output. This
circuit configuration is used for the PCM4201EVM
evaluation module.
40.2
Ω
40.2
Ω
100pF
100pF
NOTE: U1 = OPA2134 or equivalent.
V
IN
+
V
IN
−
0.022
µ
F
2.49k
Ω
2.49k
Ω
10k
Ω
10k
Ω
+
R2
R1
U1A
U1B
10
µ
F
to 100
µ
F
+5V
10
µ
F0.1
µ
F
Analog
Input
C1
Figure 12. Single-Ended Input Buffer Circuit
100pF
NOTE: U1 = OPA2134 or equivalent.
40.2
Ω
V
IN
+
2700pF
+
R2
R4
100pF
40.2
Ω
V
IN
−
U1A
U1B
R1
10
µ
F
to 100
µ
F
0.1
µ
F
R3
3
2
1
Analog
Input
Ground
Lift
Switch
10
µ
F
to 100
µ
F
10k
Ω
10k
Ω
+5V
10
µ
F
1000pF
1000pF
Figure 13. Differential Input Buffer Circuit