otherwise specified) (Continued)

Application Information

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

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:

Stability vs Capacitive Load

DS012867-36

Stability vs Capacitive Load

DS012867-37

Low Noise Single Supply Preamp

DS012867-2

www.national.com

12