Table of Contents
Advertisement
98640A Analog Input Interface
that op amp is negative. Diode CR6 prevents the op amp output from driving the polarity signal any
higher. When the analog input is positive, the inverting op amp will drive its output to the negative
rail. When this happens, current will be drawn through diode CR6 and resistors R 7 and R 15; thus, the
polarity signal will be pulled low. R 15 and R 7 will prevent the voltage of the polarity signal from
going much below ground.
The 270 pf capacitor (C43) in the feedback loop of the inverting op amp is used as a low pass filter to
reduce high frequency noise in the circuit.
+5
POLARITY
------
OUTPUT
10K
270
pf
10K
I
(S!H)OUT
I
Figure 3-6. Absolute value circuit
Analog-to-Digital Converter (ADC)
The ADC (U65) receives its analog input from the absolute value circuit and converts it to a digital
value. The converter will do a 12-bit analog-to-digital conversion in 7 microseconds; it is used in
unipolar mode to digitize a voltage from 0 to + 10 volts, with a straight binary coded output.
3-12
Advertisement
Table of Contents
