LM13700

SNOSBW2E – NOVEMBER 1999 – REVISED MARCH 2013

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APPLICATIONS

Voltage Controlled Amplifiers

Figure 23 shows how the linearizing diodes can be used in a voltage-controlled amplifier. To understand the

input biasing, it is best to consider the 13 k

Ω resistor as a current source and use a Thevenin equivalent circuit

as shown in Figure 24. This circuit is similar to Figure 22 and operates the same. The potentiometer in Figure 23

is adjusted to minimize the effects of the control signal at the output.

Figure 22. Linearizing Diodes

vs. Amplifier Bias Current graph. Larger amplitudes of input signal also improve the S/N ratio. The linearizing

diodes help here by allowing larger input signals for the same output distortion as shown by the Distortion vs.

(Figure 23) until the output distortion is below some desired level. The output voltage swing can then be set at

Although the noise contribution of the linearizing diodes is negligible relative to the contribution of the amplifier's

Figure 23. Voltage Controlled Amplifier

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