SLOS358C September 2011 – April 2020 THS4531
The THS4531 is designed for the nominal value of RF to be 2 kΩ. This gives excellent distortion performance, maximum bandwidth, best flatness, and best pulse response. It also loads the amplifier. For example, in gain of 1 with RF = RG = 2 kΩ, RG to ground, and VOUT+ = 4 V, 1 mA of current will flow through the feedback path to ground. In low power applications, it is desirable to reduce this current by increasing the gain setting resistors values. Using larger value gain resistors has two primary side effects (other than lower power) due to their interaction with the device and PCB parasitic capacitance:
Figure 76 shows the small signal frequency response for gain of 1 with RF and RG equal to 2 kΩ, 10 kΩ, and 100 kΩ. The test was done with RL = 2 kΩ. Due to loading effects of RL, lower values may reduce the peaking, but higher values will not have a significant effect.
As expected, larger value gain resistors cause lower bandwidth and peaking in the response (peaking in frequency response is synonymous with overshoot and ringing in pulse response).