OA1ZHA datasheet(17/35 Pages) STMICROELECTRONICS

17 / 35 page

OA1ZHA, OA2ZHA, OA4ZHA

Application information

DocID025994 Rev 2

17/35

Application information

5.1

Operation theory

The OA1ZHA, OA2ZHA and OA4ZHA are high precision CMOS op amp. They achieve a

low offset drift and no 1/f noise thanks to their chopper architecture. Chopper-stabilized

amps constantly correct low-frequency errors across the inputs of the amplifier.

Chopper-stabilized amplifiers can be explained with respect to:

Time domain

Frequency domain

5.1.1

Time domain

The basis of the chopper amplifier is realized in two steps. These steps are synchronized

thanks to a clock running at 400 kHz.

Figure 38: Block diagram in the time domain (step 1)

Figure 39: Block diagram in the time domain (step 2)

Figure 38: "Block diagram in the time domain (step 1)" shows step 1, the first clock cycle,

where Vio is amplified in the normal way.

Figure 39: "Block diagram in the time domain (step 2)" shows step 2, the second clock

cycle, where Chop1 and Chop2 swap paths. At this time, the Vio is amplified in a reverse

way as compared to step 1.

At the end of these two steps, the average Vio is close to zero.

The A2(f) amplifier has a small impact on the Vio because the Vio is expressed as the input

offset and is consequently divided by A1(f).

OA1ZHA Datasheet(PDF) 17 Page - STMicroelectronics