lmc2001 National Semiconductor Corporation, lmc2001 Datasheet - Page 7

• Manufacturer Part Number: lmc2001
• Description: High Precision, 6mhz Rail-to-rail Output Operational Amplifier
• Manufacturer: National Semiconductor Corporation

Application Notes
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
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
case ( Figure 5 , inverting operation) and tied to a small non-
critical negative bias in another ( Figure 6 , non-inverting op-
FIGURE 2.
FIGURE 3.
-
terminal to be grounded in one
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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 4. Single Supply Strain- Gauge Amplifier
FIGURE 5. Inverting Composite Amplifier
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