LMC272 Datasheet, PDF (12/16 Pages) National Semiconductor (TI) – CMOS Dual Low Cost Rail to Rail Output Operational Amplifier

Typical Performance Characteristics (V_S = +5V, single supply, T_A = 25˚C, and R_L to ground unless
otherwise specified) (Continued)
Stability vs Capacitive Load
Stability vs Capacitive Load
DS012867-36
Application Information
Low Noise Single Supply Preamp
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It is generally difficult to find already existing solutions in the
market which are single supply and low noise. The circuit
above is a low noise single supply preamp using the
LMC272. It utilizes the feature of input common mode volt-
age range to ground to achieve zero-volt-in zero-volt-out
performance and uses the RR output swing to achieve maxi-
mum dynamic range. By introducing a differential pair oper-
ating at high bias current as the front end, the equivalent in-
put noise voltage, e_n, is reduced. The gain is 1 + R5/R6
DS012867-2
which is a 1000 in this case. There is an inherent trade off
between noise voltage and power consumption, input bias
current, and input noise current. Input equivalent noise cur-
rent is inconsequential if the source impedance is small. R1
can be adjusted to vary bias current. To avoid saturation, R3
and R4 should be set such that Q1 and Q3 collector voltages
do not exceed 0.5V. Table 1 shows typical noise data for two
different R1 settings:
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