Datasheet

OPA692
16
SBOS236E
www.ti.com
DELAY-EQUALIZED LOW-PASS FILTER
The circuit in Figure 6 realizes a 5th-order Butterworth low-
pass filter with a –3dB bandwidth of 20MHz and group delay
equalization. This filter is based on the KRC active filter
topology using amplifiers with a fixed positive gain ≥ 1.
The OPA692 makes a good amplifier for this type of filter. The
first stage is the group delay equalizer, which is based on a
gain of –1. The second stage has a high-Q pole, uses a gain
of +2 for minimum component sensitivity, and also produces a
real pole. The last stage has a low-Q pole, and uses a gain of
+1 for minimum component sensitivity.
The component values have been predistorted to compensate
for the op amps parasitic effects. The low-Q pole section was
placed last to minimize noise peaking in the passband, while
maintaining good dynamic range performance.
PRECISION VOLTAGE BUFFER
The precision buffer in Figure 7 combines the DC precision
and low 1/f noise of the OPA227 with the high-speed perfor-
mance of the OPA692. The 80.6kΩ resistor makes the high-
frequency and low-frequency nominal gains equal. The
OPA692 takes over from the OPA227 at approximately 32kHz.
OPA692
115Ω
402Ω 49.9Ω 105Ω 226Ω402Ω
100pF
220pF
56pF
27pF
V
IN
V
OUT
OPA692
402Ω
402Ω
95.3Ω 226Ω
68pF
39pF
OPA692
402Ω
402Ω
(Open)
FIGURE 7. Precision Wideband, Unity-Gain Buffer.
OPA227
OPA692
402Ω402Ω
80.6kΩ
200Ω
V
IN
V
OUT
–5V
+5V
200Ω
2.7nF
2.7nF
FIGURE 6. Butterworth LP Filter with Delay Equalization.
DESIGN-IN TOOLS
DEMONSTRATION FIXTURES
Two printed circuit boards (PCBs) are available to assist in
the initial evaluation of circuit performance using the OPA692
in its two package options. Both of these are offered free of