Inpact of input current spikes on real applications

AN4587

8/14

DocID026923 Rev 1

2

Inpact of input current spikes on real applications

The input bias current spikes generated by the chopper architecture, occur at an equivalent

high frequency (several GHz) because of their sharp edges. The TSZ121 presents a

GBP = 400 kHz. Consequently, these input current spikes are not seen on the output of the

TSZ121 when used in closed loop configuration because the device filters them.

Nevertheless, the input current spikes might affect what is placed before the TSZ121.

2.1

High impedance input

Generally, special care must be taken with the input current of an op amp when we use a

high impedance sensor to limit the error on the input.

In this case, input current spikes might potentially disturb the sensor.

In figures 12 through 16 below, several simulations have been made to emulate a sensor by

changing the Rin_load seen by the input of the TSZ121.

Figure 12. Iib spike vs input impedance

Figure 13. Rin_load = 1 kΩ

Figure 14. Rin_load = 10 kΩ