LMV821-N_16 Datasheet, PDF (24/46 Pages) Texas Instruments – Single/Dual/Quad Low Voltage, Low Power, R-to-R Output, 5 MHz Op Amps

LMV821-N, LMV822-N, LMV822-N-Q1, LMV824-N, LMV824-N-Q1
SNOS032H – AUGUST 1999 – REVISED APRIL 2014
Typical Applications (continued)
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300 Hz High-Pass Active Filter with a Butterworth Response and a Pass Band Gain of Times Two
Figure 45. Dual Active Amplifier High-Pass Filter
8.2.4.1 Design Requirements
The LMV822/24 bring economy and performance to DAAFs. The low-pass and the high-pass filters of Figure 44
and Figure 45 (respectively), offer one key feature: excellent sensitivity performance. Good sensitivity is when
deviations in component values cause relatively small deviations in a filter's parameter such as cutoff frequency
(Fc). Single amplifier active filters like the Sallen-Key provide relatively poor sensitivity performance that
sometimes cause problems for high production runs; their parameters are much more likely to deviate out of
specification than a DAAF would. The DAAFs of Figure 44 and Figure 45 are well suited for high volume
production.
8.2.4.2 Detailed Design Procedure
Active filters are also sensitive to an op amp's parameters -Gain and Bandwidth, in particular. The LMV822/24
provide a large gain and wide bandwidth. And DAAFs make excellent use of these feature specifications.
Single Amplifier versions require a large open-loop to closed-loop gain ratio - approximately 50 to 1, at the Fc of
the filter response.
In addition to performance, DAAFs are relatively easy to design and implement. The design equations for the
low-pass and high-pass DAAFs are shown below. The first two equation calculate the Fc and the circuit Quality
Factor (Q) for the LPF (Figure 44). The second two equations calculate the Fc and Q for the HPF (Figure 45).
(4)
To simplify the design process, certain components are set equal to each other. Refer to Figure 44 and
Figure 45. These equal component values help to simplify the design equations as follows:
(5)
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