AN4071 datasheet(11/27 Pages) STMICROELECTRONICS

11 / 27 page

AN4071

Datasheet parameters

Doc ID 022939 Rev 1

11/27

Equation 2

SVR [dB] = 20

• log (|ΔVCC /ΔVIO| )

Note that, the higher CMMR and SVR are the better.

Measurement

The circuit is the same as the one used for VIO (Figure 10).

CMRR

VIO at low (L) VICM rail and VIO at high (H) VICM rail are measured

then CMRR = 20

• log [(VICM(H) - VICM(L)) / (|VIO(H)-VIO(L)|)]

SVR

VIO at low VCC and VIO at high VCC are measured

then SVR = 20

• log [(VCC(H)- VCC(L)) / (| VIO(H)-VIO(L)|)]

3.4

Voltage gain

Voltage gain AVD indicates the overall device gain. Higher gain means better small input

signal resolving capability which can be an advantage in certain applications. Common

comparators have an AVD in the range of 200 V/mV (106 dB). 1 mV input signal amplified by

106 dB leads to theoretical amplitude of 200 V. In reality, the output signal swing is limited by

VCC. Note that the AVD doesn’t affect external hysteresis as the output is always in high or

low state and never between (unlike an operational amplifier, a comparator is not used in its

linear region).

3.5

Propagation delay

Propagation delay TPD is one of the key parameters for many applications because it limits

the maximal input frequency which can be processed. Voltage comparison of analog signals

requires a minimum amount of time.

TPD is defined as the time difference between the moment the input signal crossing the

reference voltage and the moment the output state changes (usually when the output signal

crosses 50% of VCC, if nothing is specified).

A graphical interpretation is shown in Figure 12 and 13. For TPLH an input square signal

from -100 mV to +VOV, called overdrive voltage and referenced to VICM + VTRIP+, is applied

on the non-inverting input. The inverting input is connected at VICM voltage. Initial signal

condition 100 mV below VICM +VTRIP+ ensures a sufficient saturation for the input stage. For

the falling edge propagation delay measurement (TPHL), the input signal goes from

+100 mV to -VOV referenced to VICM + VTRIP-.

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