OP292/OP492 Data Sheet
SINGLE-SUPPLY ULTRASONIC
CLAMPING/LIMITING RECEIVER AMPLIFIER
Figure 42 shows an ultrasonic receiver amplifier using the
nonlinear impedance of low cost diodes to effectively control
the gain for wide dynamic range. This circuit amplifies a 40 kHz
ultrasonic signal through a pair of low cost clamping amplifiers
before feeding a band-pass filter to extract a clean 40 kHz signal
for processing.
The signal is ac-coupled into the false-ground bias node by
virtue of the capacitive piezoelectric sensing element. Rather
than using an amplifier to generate a supply splitting bias, the
false ground voltage is generated by a low cost resistive voltage
divider.
Each amplifier stage provides ac gain while passing on the dc
self-bias. As long as the output signal at each stage is less than
the forward voltage of a diode, each amplifier has unrestricted
gain to amplify low level signals. However, as the signal strength
increases, the feedback diodes begin to conduct, shunting
the feedback current, and thus reducing the gain. Although
distorting the waveform, the diodes effectively maintain a
relatively constant amplitude even with large signals that
otherwise would saturate the amplifier. In addition, this design
is considerably more stable than the feedback type AGC.
The overall circuit has a gain range from −2 to −400, where the
inversion comes from the band-pass filter stage. Operating with
a Q of 5, the filter restores a clean, undistorted signal to the output.
The circuit also works well with 5 V supply systems.
12V
600kΩ
1MΩ
RECEIVER
PANASONIC
EFR-R
TB40K2
12V
390kΩ
10kΩ
0.01µF
7.5V
12V
100kΩ
10kΩ
0.01µF
14kΩ
0.01µF
6.04kΩ
68pF
1µF
12V
600kΩ
1MΩ
7.5V
V
OUT
68pF
1/4
OP492
1/4
OP492
1/4
OP492
00310-042
56.2kΩ
Figure 42. 40 kHz Ultrasonic Clamping/Limiting Receiver Amplifier
PRECISION SINGLE-SUPPLY VOLTAGE
COMPARATOR
The OP292/OP492 have excellent overload recovery characteristics,
making them suitable for precision comparator applications.
Figure 43 shows the saturation recovery characteristics of the
OP492. The amplifier exhibits very little propagation delay. The
amplifier compares a signal to precisely <0.5 mV offset error.
2kΩ
1kΩ
20kΩ
2.21kΩ
+5V
3V p-p
–15V
1V
90
100
10
5µs5V
0%
OP492
00310-043
Figure 43. OP492 Has Fast Overload Recovery for Comparator Applications
PROGRAMMABLE PRECISION WINDOW
COMPARATOR
The OP292/OP492 can be used for precise level detection,
such as in test equipment where a signal is measured within a
range (see Figure 44). A pair of 12-bit DACs sets the threshold
voltage level. The DACs have serial interface, which minimizes
interconnection requirements. The DAC8512 has a control
resolution of 1 mV/bit. Therefore, for 5 V supply operation, the
maximum DAC output is 4.095 V. However, the OP292 accepts
a maximum input of 4.0 V.
1
2
3
4
8
7
6
5
1
2
3
4
8
7
6
5
DECODECS
CLK
SDI
LD
ANALOG
INPUT
CLR
5V
5V
2
3
6
5
7
LOW
HIGH
8
4
1
5V
1/2
OP292
1/2
OP292
CONTROL
REF
DAC8512
DAC8512
CONTROL
REF
DAC
DAC
00310-044
Figure 44. Programmable Window Comparator with
12-Bit Threshold Level Control
Rev. D | Page 16 of 20
