LMC2001 Datasheet, PDF (7/11 Pages) National Semiconductor (TI) – High Precision, 6MHz Rail-To-Rail Output Operational Amplifier

Application Notes (Continued)
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
FIGURE 2.
DS100058-A1
DS100058-21
FIGURE 4. Single Supply Strain- Gauge Amplifier
FIGURE 3.
DS100058-A0
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-
7
DS100058-30
FIGURE 5. Inverting Composite Amplifier
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