CLC408 datasheet(10/12 Pages) NSC

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where GBWPU1 is the Gain-Bandwidth Product of

U1. As R3 is made larger, fUG becomes smaller. fUG

should be large enough so that U2’s 1/f noise does not

significantly impact the output noise.

Adjust R7 so that the gain at f << fUG matches the gain at

f >> fUG.

Precision Half-Wave Rectifier

Figure 8 shows a precision half-wave rectifier. When

Vin > 0, D1 is on and D2 is off. When Vin < 0, D1 is off and

D2 is on. The second amplifier (U2) buffers Vo from the

variable output impedance of the rectifier.

The output voltage is:

Figure 8: Precision Half-Wave Rectifier

Diodes D1 and D2 need to be Schottky or PIN diodes to

minimize delay.

Set R2 = R3 to the recommended feedback resistor value

for the gain Av = -R2/R1. R2 and R3 may need to be

increased slightly to compensate for the delays through

D1 and D2.

Set R6 to the recommended feedback resistor value for

the gain Av = (1 + R6/R5).

R4 is an optional resistor; it helps isolate U2’s input from

the changing output impedance of U1.

Other configurations are possible:

1) Connect U2’s input between R3 and D2 so that

Vo ≠ 0 for Vin < 0.

2) Use an inverting gain configuration for U2 to

change the polarity of Vo.

Pick the combination that best suits your needs.

CLC408

Vin

0, V

V, V

−⋅ +

















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CLC408 Datasheet(PDF) 10 Page - National Semiconductor (TI)

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