OP292/OP492

Rev. C | Page 16 of 20

SINGLE-SUPPLY ULTRASONIC

CLAMPING/LIMITING RECEIVER AMPLIFIER

PRECISION SINGLE-SUPPLY VOLTAGE

COMPARATOR

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 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

5µs

5V

0%

OP492

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.

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.

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-RTB40K2

12V

390kΩ

10kΩ

0.01µF

7.5V

12V

100kΩ

10kΩ

0.01µF

14kΩ

0.01µF

6.04kΩ

68pF

1µF

12V

600kΩ

1MΩ

7.5V

68pF

1/4

OP492

1/4

OP492

1/4

OP492

56.2kΩ

1

2

3

4

8

7

6

5

1

2

3

4

8

7

6

5

DECODE

CS

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

Figure 42. 40 kHz Ultrasonic Clamping/Limiting Receiver Amplifier

Figure 44. Programmable Window Comparator with

12-Bit Threshold Level Control