Rainbow Electronics ADC1173 - Manual (Page 15)

Applications Information
(Continued)
The reference self-bias circuit of Figure 3 is very simple and
performance is adequate for many applications. Superior
performance can generally be achieved by driving the refer-
ence pins with a low impedance source.
By forcing a little current into or out of the top and bottom of
the ladder, as shown in Figure 4, the top and bottom refer-
ence voltages can be trimmed. The resistive divider at the
amplifier inputs can be replaced with potentiometers. The
LMC662 amplifier shown was chosen for its low offset volt-
age and low cost. Note that a negative power supply is
needed for these amplifiers as their outputs may be required
to go slightly negative to force the required reference
voltages.
10089013
FIGURE 3. Simple, Low Component Count, Self -Bias Reference application. Because of resistor tolerances, the
reference voltages can vary by as much as 6%. Choose an amplifier that can drive a dynamic capacitance (see text).
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