OP292_15 Datasheet, PDF (16/20 Pages) Analog Devices – Dual/Quad Single-Supply Operational Amplifiers

OP292/OP492
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
12V
RECEIVER
1/4
1MΩ OP492
PANASONIC
EFR-RTB40K2
390kΩ
10kΩ
0.01µF
7.5V
12V
1/4
OP492
100kΩ
10kΩ
0.01µF
68pF
14kΩ
68pF
56.2kΩ
1/4
OP492
V_OUT
6.04kΩ
0.01µF
12V
600kΩ
7.5V
1µF
1MΩ
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.
1V
100
90
+5V
1kΩ
3V p-p _OP492
2kΩ
–15V
10
2.21kΩ
20kΩ
0%
5V
5µs
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.
CS
CLK
5V
DECODE
DAC8512
1
8
REF DAC
2
7
3 _{CONTROL 6}
5V
3
8
1/2 1
2 ^OP292 _HIGH
4
SDI
4
5
LD
CLR
5V
DAC8512
1
8
REF DAC
2
7
3 _CONTROL 6
4
5
6
1/2
5 ^OP292
7
LOW
ANALOG
INPUT
Figure 44. Programmable Window Comparator with
12-Bit Threshold Level Control
Rev. C | Page 16 of 20