THS3001

RECOMMENDED FEEDBACK AND GAIN RESISTOR VALUES

The THS3001 is fabricated using Texas Instruments 30-V complementary bipolar process, HVBiCOM. This

process provides the excellent isolation and extremely high slew rates that result in superior distortion

characteristics.

As with all current-feedback amplifiers, the bandwidth of the THS3001 is an inversely proportional function of the

value of the feedback resistor (see Figures 26 to 34). The recommended resistors for the optimum frequency

response are shown in Table 1. These should be used as a starting point and once optimum values are found,

1% tolerance resistors should be used to maintain frequency response characteristics. For most applications, a

feedback resistor value of 1 k

Ω is recommended - a good compromise between bandwidth and phase margin

that yields a 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 independent 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.

Table 1. Recommended Resistor Values for Optimum

Frequency Response

GAIN

1

1 k

Ω

1 k

Ω

2, -1

680

Ω

750

Ω

2

620

Ω

620

Ω

5

560

Ω

620

Ω

OFFSET VOLTAGE

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

Figure 48. Output Offset Voltage Model

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