LMC2001ACM5 datasheet(7/11 Pages) NSC

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Application Notes (Continued)

This Strain-Gauge (

Figure 4) amplifier provides high gain

(1006 or 60 dB) with very low offset and drift. Using the resis-

tors tolerance as shown, the worst case CMRR will be

greater than 90 dB. The common-mode gain is directly re-

lated to the resistor mismatch and is independent of the dif-

ferential gain that is set by R3. The worst case common-

mode gain is −54 dB. This gain becomes even lower,

improving CMRR, if the resistor ratio matching is improved.

Extending Supply Voltages and Output Swing by Using

a Composite Amplifier Configuration:

In cases where substantially higher output swing is required

with higher supply voltages, arrangements like the ones

shown in

Figure 5, and Figure 6 could be used (pin numbers

shown are for SO-8 package). These configurations utilize

the excellent DC performance of the LMC2001 while at the

same time allow the superior voltage and frequency capabili-

ties of the LM6171 to set the dynamic performance of the

overall amplifier. For example, it is possible to achieve ±12V

output swing with 300MHz of overall GBW (Av=100) while

keeping the worst case output shift due to Vos less than

4mV. The LMC2001 output voltage is kept at about mid-point

of it’s overall supply voltage and it’s input common mode

voltage range allows the V

- terminal to be grounded in one

case (

Figure 5, inverting operation) and tied to a small non-

critical negative bias in another (

Figure 6, non-inverting op-

eration). Higher closed loop gains are also possible with a

corresponding reduction in realizable bandwidth. Table 1

shows some other closed loop gain possibilities along with

the measured performance in each case

Application Circuits

DS100058-A1

FIGURE 2.

DS100058-A0

FIGURE 3.

DS100058-21

FIGURE 4. Single Supply Strain- Gauge Amplifier

DS100058-30

FIGURE 5. Inverting Composite Amplifier

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