+V

ADC

-

+

LMP7701

ADC122S021

SDO

LM7705

+V

B

A

-V

LM7705

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SNVS420B – NOVEMBER 2008 – REVISED MARCH 2013

Figure 32. Typical True Zero Output Voltage Application with/without LM7705

The output voltage of the LMP7701 is converted to the digital domain using an ADC122S021. This is an 12 bit

analog to digital converter with a serial data output. Data processing and graphical displaying is done with a

computer. The negative power supply pin of the op amp can be connected to ground level or to the output of the

negative bias generator, to demonstrate the effect at the output voltage range of the op amp.

The key specifications of the used components are given in the next part of the section.

Supply Voltage/Reference Voltage

Supply voltage

+5V

ADC Voltage Reference

+5V

LMP7701

18 mV

50 mV

LM7705

Output voltage ripple

Output voltage noise

ADC

Type

ADC122S021

Resolution

12 bit

Quantization level

5V/4096 = 1.2mV

Measurement Results

The output voltage range of the LMP7701 has been measured, especially the range to ground level. A small DC

measured over a given time period, when its negative supply pin is connected to ground level or connected to

the output of the LM7705.

Figure 33A and Figure 33B show the digitized output voltage of the LMP7701 op amp.

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