ADC0804LCWM datasheet(33/56 Pages) TI1

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ADC0801, ADC0802, ADC0803, ADC0804, ADC0805

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SNOSBI1C – NOVEMBER 2009 – REVISED JUNE 2015

R2 = 49.5 R1

Switches are LMC13334 CMOS analog switches.

The 9 resistors used in the auto-zero section can be ±5% tolerance.

Figure 43. Gain of 100 Differential Transducer Preamp

where

•

IX is the current through resistor RX

(5)

All of the offset error terms can be cancelled by making ±IXRX= VOS1 + VOS3 − VOS2. This is the principle of this

auto-zeroing scheme.

The INS8080A uses the 3 I/O ports of an INS8255 Programable Peripheral Interface (PPI) to control the auto

zeroing and input data from the ADC0801 as shown in Figure 44. The PPI is programmed for basic I/O operation

(mode 0) with Port A being an input port and Ports B and C being output ports. Two bits of Port C are used to

alternately open or close the 2 switches at the input of the preamp. Switch SW1 is closed to force the preamp’s

differential input to be zero during the zeroing subroutine and then opened and SW2 is then closed for

conversion of the actual differential input signal. Using 2 switches in this manner eliminates concern for the ON

resistance of the switches as they must conduct only the input bias current of the input amplifiers.

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ADC0804LCWM Datasheet(PDF) 33 Page - Texas Instruments