Application Note

AN-763

Rev. C | Page 3 of 8

HALF WAVE, FULL WAVE RECTIFIER

Rectifying circuits are used in a multitude of applications. One

of the most popular uses is in the design of regulated power

supplies where a rectifier circuit is used to convert an input

sinusoid to a unipolar output voltage. There are some potential

problems for amplifiers used in this manner.

When the input voltage VIN is negative, the output is zero.

When the magnitude of VIN is doubled at the input of the op

amp, this voltage could exceed the power supply voltage which

would damage the amplifiers permanently. The op amp must

come out of saturation when VIN is negative. This delays the

output signal because the amplifier needs time to enter its

linear region.

The ADA4610-2 has a very fast overdrive recovery time, which

makes it a great choice for rectification of transient signals. The

symmetry of the positive and negative recovery time is also very

important in keeping the output signal undistorted.

8

4

2

1

3

1/2

ADA4610-2

4

8

5

7

6

2/2

ADA4610-2

R2

10k

Ω

R3

10k

Ω

R1

1k

Ω

OUT A

(HALF WAVE)

OUT B

(FULL WAVE)

5V

5V

VIN

3V p-p

+

–

Figure 2. Half Wave and Full Wave Rectifier

TIME (1mS/DIV)

Figure 3. Half Wave Rectifier Signal (Output A)

TIME (1mS/DIV)

Figure 4. Full Wave Rectifier Signal (Output B)

Figure 2 is a typical representation of a rectifier circuit. The first

stage of the circuit is a half wave rectifier. When the sine wave

applied at the input is positive, the output follows the input

response. During the negative cycle of the input, the output tries

to swing negative to follow the input, but the power supplies

restrains it to zero. Similarly, the second stage is a follower

during the positive cycle of the sine wave and an inverter during

the negative cycle. Figure 3 and Figure 4 represents the signal

response of the circuit at Output A and Output B, respectively.

HIGH GAIN COMPOSITE AMPLIFIER

VEE

VCC

R1

1k

Ω

VCC

VEE

VIN

99k

Ω

R2

V+

V–

V+

V–

R3

R4

99k

Ω

1k

Ω

U5

1/2

ADA4661-2

1/2

ADA4661-2

Figure 5. High Gain Composite Amplifier

A composite amplifier can provide a very high gain in appli-

cations where high closed-loop dc gain is needed. The high gain

achieved by the composite amplifier comes at the expense of a

loss in phase margin.

Placing a small capacitor, CF, in the feedback loop and in

parallel with R2 improves the phase margin. For the circuit

of Figure 5, picking a CF = 50 pF yields a phase margin of

about 45°.