OPA2832 Datasheet, PDF (22/37 Pages) National Semiconductor (TI) – Dual, Low-Power, High-Speed, Fixed-Gain Operational Amplifier

OPA2832
SBOS327C – FEBRUARY 2005 – REVISED AUGUST 2008 ............................................................................................................................................. www.ti.com
0.1µF
V_I
3kΩ
205Ω
2kΩ
866Ω
300pF
+5V
470pF
1/2
OPA2832
400Ω
2V_I
1MHz, 2nd−Order
Butterworth Filter
400Ω
0.1µF
Figure 66. Single-Supply, High-Frequency Active Filter
DIFFERENTIAL LOW-PASS FILTERS
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 119Ω. This is
implemented in Figure 67 as the parallel combination
of the two 238Ω resistors on each half of the
differential input as part of the DC biasing network. If
the BUF602 is removed, these resistors should be
collapsed back to a single 119Ω input resistor.
150pF
+5V
0.1µF
238Ω
506Ω
+5V
1 /2
O PA 283 2
238Ω
100pF ^400Ω
400Ω
5kΩ
2.5V
V
I
V_I
BUF602
V_O
0.1µF 5kΩ
238Ω
100pF
400Ω
400Ω
0.1µF
238Ω
506Ω
1/2
O PA 28 32
150pF
Figure 67. Single-Supply, 5MHz, 2nd-Order,
Low-Pass Sallen-Key Filter
22
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