OP291GP View Datasheet(PDF) - Analog Devices

Part Name

Description

View to exact match

OP291GP

Micropower Single-Supply Rail-to-Rail Input/Output Op Amps

Analog Devices 

OP191/OP291/OP491

R2

2.67k⍀

+3V

2 11

VIN

1/4

OP491

1

3 4 A1

R1

2.67k⍀

C1

1␮F

R3

2.67k⍀

R6

100k⍀

C3

2␮F

(1␮F؋2)

C2

1␮F

R4

2.67k⍀

R5

1.33k⍀

(2.67k⍀÷2)

R11

100k⍀

C5

+3V

R9

1M⍀

C4

1␮F

0.01␮F

9

1/4

OP491

8

10

A3

R10

1M⍀

R12

499⍀

C6

1.5V

1␮F

5

1/4

OP491

7

6

A2

R8

1k⍀

R7

1k⍀

VOUT

Figure 13. A +3 V Single-Supply, 50 Hz/60 Hz Active Notch

Filter with False Ground

Amplifier A3 is the heart of the false-ground bias circuit. It

simply buffers the voltage developed by R9 and R10 and is the

reference for the active notch filter. Since the OP491 exhibits a

rail-to-rail input common-mode range, R9 and R10 are chosen

to split the +3 V supply symmetrically. An in-the-loop compen-

sation scheme is used around the OP491 that allows the op amp

to drive C6, a 1 µF capacitor, without oscillation. C6 maintains

a low impedance ac ground over the operating frequency range

of the filter.

The filter section uses a pair of OP491s in a twin-T configura-

tion whose frequency selectivity is very sensitive to the relative

matching of the capacitors and resistors in the twin-T section.

Mylar is the material of choice for the capacitors, and the rela-

tive matching of the capacitors and resistors determines the

filter’s passband symmetry. Using 1% resistors and 5% capaci-

tors produces satisfactory results.

Single-Supply Half-Wave and Full-Wave Rectifiers

An OP191 family configured as a voltage follower operating on

a single supply can be used as a simple half-wave rectifier in

low-frequency (<2 kHz) applications. A full-wave rectifier can

be configured with a pair of OP291s as illustrated in Figure 14.

The circuit works in the following way: When the input signal is

above 0 V, the output of amplifier A1 follows the input signal.

Since the noninverting input of amplifier A2 is connected to

A1’s output, op amp loop control forces the A2’s inverting input

to the same potential. The result is that both terminals of R1 are

equipotential; i.e., no current flows. Since there is no current

flow in R1, the same condition exists upon R2; thus, the output

of the circuit tracks the input signal. When the input signal is

below 0 V, the output voltage of A1 is forced to 0 V. This con-

dition now forces A2 to operate as an inverting voltage follower

because the noninverting terminal of A2 is at 0 V as well. The

output voltage at VOUTA is then a full-wave rectified version of

the input signal. If needed, a buffered, half-wave rectified version

of the input signal is available at VOUTB.

VIN

2V p-p

<2kHz

R1

100k⍀

+5V

3

8

1/2

OP291

1

2

4 A1

R2

100k⍀

6

1/2

OP291

7

5

A2

1V

VIN

(1V/DIV) 100

90

500mV

VOUT A

FULL-WAVE

RECTIFIED

OUTPUT

VOUT B

HALF-WAVE

RECTIFIED

OUTPUT

VOUTB

(0.5V/DIV)

10

VOUTA 0%

(0.5V/DIV)

500mV

200␮s

TIME – 200␮s/DIV

Figure 14. Single-Supply Half-Wave and Full-Wave

Rectifiers Using an OP291

REV. A

–17–

Share Link: