TSZ181 datasheet(18/43 Pages) STMICROELECTRONICS

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Figure 48. Vio cancellation principle

Step 1

S tep 1

Step 2

S tep 2

Vio

Time

Vio

The low pass filter averages the output value resulting in the cancellation of the Vio offset.

The 1/f noise can be considered as an offset in low frequency and it is canceled like the Vio, thanks to the chopper

technique.

5.1.2

Frequency domain

The frequency domain gives a more accurate vision of chopper-stabilized amplifier architecture.

Figure 49. Block diagram in the frequency domain

Vinn

Vi np

Vos + Vn

Chop1

A(f)

Chop2

Filter

A(f)

Vout

The modulation technique transposes the signal to a higher frequency where there is no 1/f noise, and

demodulate it back after amplification.

According to Figure 49. Block diagram in the frequency domain, the input signal Vin is modulated once

(Chop1) so all the input signal is transposed to the high frequency domain.

The amplifier adds its own error (Vio (output offset voltage) + the noise Vn (1/f noise)) to this modulated

signal.

This signal is then demodulated (Chop2), but since the noise and the offset are modulated only once, they

are transposed to the high frequency, leaving the output signal of the amplifier without any offset and low

frequency noise. Consequently, the input signal is amplified with a very low offset and 1/f noise.

To get rid of the high frequency part of the output signal (which is useless) a low pass filter is implemented.

To further suppress the remaining ripple down to a desired level, another low pass filter may be added externally

on the output of the TSZ18x.

5.2

Operating voltages

The TSZ18x device can operate from 2.2 to 5.5 V. The parameters are fully specified for 2.2 V, 3.3 V, and 5 V

power supplies. However, the parameters are very stable in the full VCC range and several characterization

curves show the TSZ18x device characteristics at 2.2 V and 5.5 V. Additionally, the main specifications are

guaranteed in extended temperature ranges from -40 to 125 °C.

5.3

Input pin voltage ranges

The TSZ18x device has internal ESD diode protection on the inputs. These diodes are connected between the

input and each supply rail to protect the input MOSFETs from electrical discharge.

TSZ181, TSZ182

Operating voltages

DS11863 - Rev 5

page 18/43

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