LMP91200

+

±

pH

BUFFER

VCM

BUFFER

VDD

VOUT

VOCM

VREF

GND

VCMHI

GUARD1

GUARD2

INP

VCM

14

LMP91200

SNAS571E – JANUARY 2012 – REVISED FEBRUARY 2016

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7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 pH Buffer

The pH Buffer is a unity gain buffer with a input bias current in the range of tens fA at room temperature. Its very

low bias current introduces a negligible error in the measurement of the pH. The ph buffer is provided with 2

guard pins (GUARD1, GUARD2) in order to minimize the leakage of the input current and to make the design of

a guard ring easy.

7.3.2 VCM Buffer

Both buffered and unbuffered version of the common-mode voltage are available respectively at the VCM pin

and VCMHI pin. A copy of the buffered version is present at VOCM pin in case of differential measurement.