Datasheet

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Differential ADC Driver
Bandpass Filter
0
-5
-10
-15
-20
-25
-30
-35
-40
10k 100k 1M 10M 100M
Gain(dB)
Frequency(Hz)
1/2
OPA2652
1/2
OPA2652
24.9W
143W
140W
2.10kW
1.0nF1.0nF
V
IN
+5V
-5V
2.2nF
1.30kW
24.9W
200W
107W
225W
20.0W
158W
150pF12pF
2.7nF
+5V
-5V
180pF
100W
100pF
1%Resistors
5%Capacitors
18pF
V
OUT
OPA2652
SBOS125A – JUNE 2000 – REVISED MAY 2006
The circuit on the front page shows an OPA2652
driving the ADS807 analog-to-digital converter (ADC)
differentially, at a gain of +2V/V. The outputs are
AC-coupled to the converter to adjust for the
difference in supply voltages. The 133 Ω resistors at
the noninverting inputs minimize DC offset errors.
The differential topology minimizes even-order
distortion products, such as second-harmonic
distortion.
Figure 31 shows a single OPA2652 implementing a
sixth-order bandpass filter. This filter cascades two
second-order Sallen-Key sections with transmission
Figure 30. Nominal Filter Response
zeros, and a double real pole section. It has 0.3dB of
ripple, –3dB frequencies of 450kHz and 11MHz, and
–23dB frequencies of 315kHz and 16MHz. The
20.0 Ω resistor isolates the first OPA2652 output from
capacitive loading. This configuration improves
stability with minimal impact on the filter response.
Figure 30 shows the nominal response simulated by
SPICE.
Figure 31. Bandpass Filter
11
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