RC4156 View Datasheet(PDF) - Fairchild Semiconductor

Part Name

Description

Manufacturer

RC4156

High Performance Quad Operational Amplifiers

Fairchild Semiconductor 

PRODUCT SPECIFICATION

RC4156/RC4157

These equations suggest a tuning sequence where ω is first

trimmed via R1 or R2, then Q is trimmed by varying R7

and/or R3. An important advantage of the state-variable

bandpass filter is that Q can be varied without affecting

center frequency ω0.

This analysis has assumed ideal op amps operating within

their linear range, which is a valid design approach for a

reasonable range of ω0 and Q. At extremes of ω0 and at high

values of Q, the op amp parameters become significant. A

rigorous analysis is very complex, but some factors are par-

ticularly important in designing active filters.

1. The passive component values should be chosen such

that all op amps are operating within their linear region

for the anticipated range of input signals. Slew rate, out-

put current rating, and common-mode input range must

be considered. For the integrators, the current through

the feedback capacitor (I = C dV/dt) should be included

in the output current computations.

2. From the equation for Q, it should seem that infinite Q

could be obtained by making R7 zero. But as R7 is made

small, the Q becomes limited by the op amp gain at the

frequency of interest. The effective closed-loop gain is

being increased directly as R7 is made smaller, and the

ratio of open-loop gain to closed-loop gain is becoming

less. The gain and phase error of the filter at high Q is

very dependent on the op amp open-loop gain at w0.

3. The attenuation at extremes of frequency is limited by

the op amp gain and unity-gain bandwidth. For integra-

tors, the finite open-loop op amp gain limits the accu-

racy at the low-end. The open-loop roll-off of gain limits

the filter attenuation at high frequency.

The RC4156 quad operational amplifier has much better fre-

quency response than a conventional 741 circuit and is ideal

for active filter use. Natural frequencies of up to 10 kHz are

readily achieved and up to 20 kHz is practical for some con-

figurations. Q can range up to 50 with very good accuracy

and up to 500 with reasonable response. The extra gain of the

RC4156 at high frequencies gives the quad op amp an extra

margin of performance in active-filter circuits.

Schematic Diagram (1/4 shown)

(2,6,9,13)

- Input

+ Input

(3,5,10,12)

R1

4900

Q2

Q4

Q5

Q7

Q8

Q9

65-0735

R3

18K

Q3

R9

30

Q13

R5

30K

D2

Q12

Q16

C1

Q10

R4

22K

Q17

Q11

(4)

+V s

Q1

Q15

R6

20 R8

150

(1,7,8,14)

Outputs

To

Next

F1

Amplifier

R7

20

Q6

Q14

D1

R2

10K

(11)

-Vs

10

REV. 1.0.1 6/13/01

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