Datasheet

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OPA2832
400
Ω
2k
Ω
400
Ω
+5V
3k
Ω
2V
I
V
I
300pF
0.1
µ
F
1MHz, 2nd−Order
Butterworth Filter
470pF
866
Ω
205
Ω
0.1
µ
F
DIFFERENTIAL LOW-PASS FILTERS
506Ω
0.1µF
506Ω
238Ω
5k
Ω
5kΩ
238Ω
0.1µF
V
I
238
Ω
238Ω
BUF602
150pF
150pF
100pF
100pF
0.1
µ
F
+5V
2.5V
V
O
V
I
+5V
1 /2
O P A2 83 2
1 / 2
O P A2 8 32
400
Ω
400Ω
400
Ω
400Ω
OPA2832
SBOS327C – FEBRUARY 2005 – REVISED AUGUST 2008 ............................................................................................................................................. www.ti.com
Figure 66. Single-Supply, High-Frequency Active Filter
The dual OPA2832 offers an easy means to
implement low-power differential active filters. On a
single supply, one way to implement a 2nd-order,
low-pass filter is shown in Figure 67 . This circuit
provides a net differential gain of 1 with a precise
5MHz Butterworth response. The signal is
AC-coupled (giving a high-pass pole at low
frequencies) with the DC operating point for the
circuit set by the unity-gain buffer — the BUF602. This
buffer gives a very low output impedance to high
frequencies to maintain accurate filter characteristics.
If the source is a DC-coupled signal already biased
into the operating range of the OPA2832 input CMR,
these capacitors and the midpoint bias may be
removed. To get the desired 5MHz cutoff, the input
resistors to the filter is actually 119 Ω . This is
implemented in Figure 67 as the parallel combination
of the two 238 Ω resistors on each half of the
Figure 67. Single-Supply, 5MHz, 2nd-Order,
differential input as part of the DC biasing network. If
Low-Pass Sallen-Key Filter
the BUF602 is removed, these resistors should be
collapsed back to a single 119 Ω input resistor.
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