The reference bias circuit of Figure 2 is very simple and the

performance is adequate for many applications. However,

circuit tolerances will lead to a wide reference voltage range.

Superior performance can generally be achieved by driving

the reference pins with a low impedance source.

The circuit of Figure 3 will allow a more accurate setting of

the reference voltages. The lower amplifier must have bipo-

lar supplies as its output voltage must go negative to force

V

course, the divider resistors at the amplifier input could be

changed to suit your reference voltage needs, or the divider

can be replaced with potentiometers for precise settings.

The bottom of the ladder (V

ground if the minimum input signal excursion is 0V. Be sure

that the driving sources can source sufficient current into the

V

these pins stable.

The LMC662 amplifier shown was chosen for its low offset

voltage and low cost.

20006232

FIGURE 2. Simple, low component count reference biasing. Because of the ladder and external resistor tolerances,

the reference voltage can vary too much for some applications.

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