LMP2014MT

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SNOSAK6B – DECEMBER 2004 – REVISED MARCH 2013

LMP2014 AS ADC INPUT AMPLIFIER

The LMP2014 is a great choice for an amplifier stage immediately before the input of an ADC (Analog-to-Digital

Converter), whether AC or DC coupled. See Figure 35 and Figure 36. This is because of the following important

characteristics:

a. Very low offset voltage and offset voltage drift over time and temperature allow a high closed-loop gain

setting without introducing any short-term or long-term errors. For example, when set to a closed-loop gain of

100 as the analog input amplifier for a 12-bit A/D converter, the overall conversion error over full operation

temperature and 30 years life of the part (operating at 50°C) would be less than 5 LSBs.

b. Fast large-signal settling time to 0.01% of final value (1.4

μs) allows 12 bit accuracy at 100 KHZ or more

sampling rate.

c. No flicker (1/f) noise means unsurpassed data accuracy over any measurement period of time, no matter

how long. Consider the following op amp performance, based on a typical low-noise, high-performance

commercially-available device, for comparison:

Op amp flatband noise = 8nV/

√Hz

1/f corner frequency = 100 Hz

AV = 2000

Measurement time = 100 sec

Bandwidth = 2 Hz

This example will result in about 2.2 mVPP (1.9 LSB) of output noise contribution due to the op amp alone,

compared to about 594

μVPP (less than 0.5 LSB) when that op amp is replaced with the LMP2014 which has

no 1/f contribution. If the measurement time is increased from 100 seconds to 1 hour, the improvement

realized by using the LMP2014 would be a factor of about 4.8 times (2.86 mVPP compared to 596 μV when

LMP2014 is used) mainly because the LMP2014 accuracy is not compromised by increasing the observation

time.

d. Copper leadframe construction minimizes any thermocouple effects which would degrade low level/high gain

data conversion application accuracy (see discussion under " The Benefits of the LMP2014" section above).

e. Rail-to-Rail output swing maximizes the ADC dynamic range in 5-Volt single-supply converter applications.

Below are some typical block diagrams showing the LMP2014 used as an ADC amplifier.

Figure 36.

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