ADC0806 National Semiconductor, ADC0806 Datasheet - Page 14

• Manufacturer Part Number: ADC0806
• Description: 500 ns A/D Converter with S/H Function and Input Multiplexer
• Manufacturer: National Semiconductor

www.national.com
Applications Information
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
FIGURE 2. Simple, low component count reference biasing. Because of the ladder and external resistor tolerances,
RB
to any voltage below the V
the reference voltage can vary too much for some applications.
BE
of the PNP transistor. Of
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14
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.
RT
pin and sink enough current from the V
RB
20006232
) may simply be returned to
RB
pin to keep