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RHF310K-01V

Rad-hard 400 µA high-speed operational amplifier

STMicroelectronics 

RHF310

3

Power supply considerations

Power supply considerations

Correct power supply bypassing is very important for optimizing the performance of the

device in high-frequency ranges. The bypass capacitors should be placed as close as

possible to the IC pins to improve high-frequency bypassing. A capacitor greater than 1 µF

is necessary to minimize the distortion. For better quality bypassing, a capacitor of 10 nF

can be added, which should also be placed as close as possible to the IC pins. The bypass

capacitors must be incorporated for both the negative and positive supply.

Figure 22. Circuit for power supply bypassing

+VCC

10 µF

+

10 nF

+

-

10 nF

-VCC

10 µF

+

AM00835

3.1

Single power supply

If you use a single-supply system, biasing is necessary to obtain a positive output dynamic

range between the 0 V and +VCC supply rails. Considering the values of VOH and VOL, the

amplifier provides an output swing from +0.9 V to +4.1 V on 1 kΩ loads.

The amplifier must be biased with a mid-supply (nominally +VCC/2) in order to maintain the

DC component of the signal at this value. Several options are possible to provide this bias

supply, such as a virtual ground using an operational amplifier or a two-resistance divider

(which is the cheapest solution). A high resistance value is required to limit the current

consumption. On the other hand, the current must be high enough to bias the non-inverting

input of the amplifier. If we consider this bias current (55 µA maximum) as 1% of the current

through the resistance divider, two resistances of 470 Ω can be used to maintain a mid

supply.

The input provides a high-pass filter with a break frequency below 10 Hz, which is

necessary to remove the original 0 V DC component of the input signal and to set it at

+VCC/2.

Figure 23 on page 12 illustrates a 5 V single power supply configuration.

A capacitor CG is added in the gain network to ensure a unity gain at low frequencies to

keep the right DC component at the output. CG contributes to a high-pass filter with Rfb//RG

and its value is calculated with a consideration of the cut-off frequency of this low-pass filter.

Doc ID 15577 Rev 3

11/22

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