RHF330 Datasheet, PDF (12/22 Pages) STMicroelectronics – Rad-hard 1 GHz low noise operational amplifier

Power supply considerations
4
Power supply considerations
RHF330
Correct power supply bypassing is very important for optimizing performance 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 10 nF capacitor can be added. It
should also be placed as close as possible to the IC pins. The bypass capacitors must be
incorporated for both the negative and the positive supply.
For example, on the RHF3xx single op-amp demonstration board, these capacitors are C6,
C7, C8, C9.
Figure 28. Circuit for power supply bypassing
+V_CC
10 µF
+
10 nF
+
-
10 nF
-V_CC
10 µF
+
AM00835
4.1
Single power supply
In the event that a single supply system is used, biasing is necessary to obtain a positive
output dynamic range between 0 V and +V_CC supply rails. Considering the values of V_OH
and V_OL, the amplifier provides an output swing from +0.9 V to +4.1 V on a 100 Ω load.
The amplifier must be biased with a mid-supply (nominally +V_CC/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, to keep a stable mid-supply, two resistances of 470 Ω can be
used.
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 +V_CC/2.
Figure 29 on page 13 illustrates a 5 V single power supply configuration for the RHF3xx
single op-amp demonstration board.
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Doc ID 15576 Rev 3