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What causes Iib spikes

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What causes Iib spikes

Figure 1 shows the chopping principle of the TSZ121 input stages. The input voltage passes

through a chopper stage driven by a clock at a frequency Fchop. On the first clock cycle

(step 1), the first MOS stage is closed and the Vio is amplified in the normal way. On the

next clock cycle, the second MOS stage is closed, and in this case, the Vio is amplified in a

reverse way compared to step1.

The average equivalent, Vio, of these two cycles is close to zero.

Figure 1. Input stage chopping principle

But, due to the switching MOS, this chopper stage injects some charge directly on the input,

resulting in current spikes on the input pins.

Figure 2 shows a snapshot scope of the input bias current measured on the TSZ121.

Figure 2. TSZ121 input bias current spike, Vcc = 5.5 V