THS6012

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SLOS226F – SEPTEMBER 1998 – REVISED JUNE 2012

resistance increases, the output resistance of the amplifier becomes less dominant at high frequencies. To

compensate for this, the feedback resistor should change. For 100-

Ω loads, it is recommended that the feedback

resistor be changed to 820

Ω for a gain of 1 and 560 Ω for a gain of 2 or -1. Although, for most applications, a

feedback resistor value of 1 k

Ω is recommended, which is a good compromise between bandwidth and phase

margin that yields a very stable amplifier.

Consistent with current feedback amplifiers, increasing the gain is best accomplished by changing the gain

resistor, not the feedback resistor. This is because the bandwidth of the amplifier is dominated by the feedback

resistor value and internal dominant-pole capacitor. The ability to control the amplifier gain independently of the

bandwidth constitutes a major advantage of current feedback amplifiers over conventional voltage feedback

amplifiers. Therefore, once a frequency response is found suitable to a particular application, adjust the value of

the gain resistor to increase or decrease the overall amplifier gain.

Finally, it is important to realize the effects of the feedback resistance on distortion. Increasing the resistance

decreases the loop gain and increases the distortion. It is also important to know that decreasing load impedance

increases total harmonic distortion (THD). Typically, the third order harmonic distortion increases more than the

second order harmonic distortion.

OFFSET VOLTAGE

The output offset voltage, (VOO) is the sum of the input offset voltage (VIO) and both input bias currents (IIB) times

the corresponding gains. The following schematic and formula can be used to calculate the output offset voltage:

Figure 40. Output Offset Voltage Model

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