K305(2004) 데이터 시트보기 (PDF) - STMicroelectronics

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K305
(Rev.:2004)

550 MHz, Low Noise Current Feedback Amplifier

STMicroelectronics 

Power Supply Considerations

TSH350

4 Power Supply Considerations

Correct power supply bypassing is very important for optimizing performance in high-frequency ranges.

Bypass capacitors should be placed as close as possible to the IC pins to improve high-frequency

bypassing. A capacitor greater than 1µF is necessary to minimize the distortion. For better quality

bypassing, a capacitor of 10nF can be added using the same implementation conditions. Bypass

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

Note: On the SO8_SINGLE_HF board, these capacitors are C6, C7, C8, C9.

Figure 30: Circuit for power supply bypassing

+VCC

10microF

+

10nF

+

-

10nF

-VCC

10microF

+

Single power supply

In the event that a single supply system is used, new biasing is necessary to assume a positive output

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

will provide an output dynamic from +0.9V to +4.1V on 100Ω load.

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 (35µA

max.) as the 1% of the current through the resistance divider to keep a stable mid-supply, two resistances

of 750Ω can be used.

The input provides a high pass filter with a break frequency below 10Hz which is necessary to remove the

original 0 volt DC component of the input signal, and to fix it at +VCC/2.

Figure 31 illustrates a 5V single power supply configuration for the SO8_S_MULTI evaluation board (see

Evaluation Boards on page 10).

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