REV. B

–12–

SSM2018T

If a symmetry trim is to be performed, it should precede the

control feedthrough trim and be done as follows:

1. Apply a 1 kHz sine wave of 10 dBu to the input with the

control voltage set for unity gain.

2. Adjust the symmetry trim potentiometer to minimize distor-

tion of the output signal.

Next the control feedthrough trim is done as follows:

1. Ground the input signal port and apply a 60 Hz sine wave

to the control port. The sine wave should have its high and

low peaks correspond to the highest gain to be used in the

application and 30 dB of attenuation, respectively. For

example, a range of 20 dB gain to 30 dB attenuation requires

that the sine wave amplitude ranges between –560 mV and

+840 mV on Pin 11.

2. Adjust the control feedthrough potentiometer to null the

signal seen at the output.

Figure 7. OVCE Follower/VCA Connection

18k

50pF

470k

500k

V+

100k

10M

CONTROL

FEEDTHROUGH

TRIM

V+

V–

INPUTS

220pF

NC

V–

1 F

1k

3k

FOR CLASS A

150k

FOR CLASS AB

NC = NO CONNECT

SYMMETRY

TRIM

V+

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

SSM2018T

18k

50pF

Figure 8. OVCE Application Circuit

Voltage Controlled Panner

An interesting circuit that is built with the OVCE building

block is a voltage controlled panner. Figure 9 shows the feed-

back connection for the circuit. Notice that the average of both

outputs is fed back to the input. Thus, the average must be

equal to the input voltage. When the control voltage is set for

fied. The result is that the control voltage causes the input to

“pan” from one output to the other. The following expressions

show how this circuit works mathematically:

V

(4)

where K varies between 0 and 1 as the control voltage is changed

for best performance. Pin 9 must be grounded. This is possible

because the feedback is constant and the adaptive network is not

needed. The VCP is the only application shown in this data

sheet where Pin 9 is grounded.

18k

18k

Figure 9. Basic VCP Connection