LM4881

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SNAS001D – SEPTEMBER 1997 – REVISED MAY 2013

Once the power dissipation equations have been addressed, the required gain can be determined from

Equation 4.

(4)

(5)

Since the desired input impedance was 20 k

assuming 5% tolerance resistors. This combination results in a nominal gain of 1.35. The final design step is to

address the bandwidth requirements which must be stated as a pair of

−3 dB frequency points. Five times away

from a

−3 dB point is 0.17 dB down from passband response assuming a single pole roll-off. As stated in the

highpass filters. Thus to obtain the desired frequency low response of 100 Hz within ±0.5 dB, both poles must be

taken into consideration. The combination of two single order filters at the same frequency forms a second order

response. This results in a signal which is down 0.34 dB at five times away from the single order filter

−3 dB

point. Thus, a frequency of 20 Hz is used in the following equations to ensure that the response is better than 0.5

dB down at 100 Hz.

(6)

(7)

smaller than the LM4881 GBWP of 18 MHz. This figure displays that if a designer has a need to design an

amplifier with a higher gain, the LM4881 can still be used without running into bandwidth limitations.

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