4. Zero-level detection
In an op-amp comparator , when the input voltage
exceeds a specified reference voltage , the output
change state.
A sine wave input voltage applied to the noninverting
input of the zero-level detector.
When the sine wave is negative , the output is at its
max. negative level.
When the sine wave crosses 0, the amplifier is driven
to its opposite state and the output goes to its max.
positive level.
5. Zero-level detection
The zero-level detector can be used as a
squaring circuit to produce a square
wave from a sine wave.
7. Non-zero-level detection
The zero-level detector can be modified to detect
voltage other than (0) by connecting a fixed
reference voltage.
A more practical arrangement using a voltage
divider to set the reference voltage as follows:
VREF = (R2/R1+R2)(+V)
9. Non-zero-level detection
(+V) is the positive op-amp supply voltage.
When the input voltage Vin is less than VREF , the
output remains at the max. negative level.
When the input voltage exceeds the reference
voltage , the output goes to its max. positive state.
13. Reducing noise effects with hysteresis
A comparator switches to one state when the
input reaches the UTP and back to the other state
when the input drops below the LTP.
The difference between the UTP and the LTP is the
hysteresis voltage.
A hysteresis is sometimes known as a Schmitt
trigger.
VHYS = VUTP - VLTP
21. Window comparator
When an input voltage is between two limits , an
upper and a lower.
The upper and lower limits are set by reference
voltages designated VU and VL.
These voltages can be established with voltage
dividers , zener diodes , or any type of voltage
source.
23. Window comparator
Vin is within the window (less than VU and greater
than VL), the VOUT is held at (0) by resistor to
ground.
When Vin goes above VU or below VL , the output of
the comparator goes to its high saturated level.
34. Averaging amplifier
The average amplifier is done by setting the ratio
Rf/R equal to the reciprocal of the number of
inputs.
To obtain the average of several numbers by first
adding the numbers and then dividing by the
amount of numbers you have.
38. Section review 14-2
1) Define summing point.
The terminal of the op-amp where the input resistors are
commonly connected.
2) What is the value of Rf/R for a five input averaging
amplifier.
1/5
3) A certain scaling adder has two inputs, one having twice
the weight of the other. If the lower input resistor value is
10kΩ, what is the value of the other input resistor?
Rf/R = 2 Rf/10kΩ =2 Rf = 20kΩ
40. integrator
Integration is the mathematical process
of finding the area under a curve.
The op-amp integrator produces an
output that proportional to the area
under the curve of the input voltage.
55. Instrumentation amplifier
It consists of three op-amp and several resistors.
Common characteristics are high input impedance
(typically 300MΩ) , high voltage gain , and
excellent CMRR (typically 100dB).
