LM13600 datasheet(13/24 Pages) NSC

13 / 24 page

Voltage Controlled Filters (Continued)

Voltage Controlled Oscillators

The classic Triangular/Square Wave VCO of

Figure 15 is

one of a variety of Voltage Controlled Oscillators which may

be built utilizing the LM13600. With the component values

shown, this oscillator provides signals from 200 kHz to below

2HzasI

C is varied from 1 mA to 10 nA. The output ampli-

tudes are set by I

A xRA. Note that the peak differential input

voltage must be less than 5V to prevent zenering the inputs.

A few modifications to this circuit produce the ramp/pulse

VCO of

Figure 16. When V

O2 is high, IF is added to IC to in-

crease amplifier A1’s bias current and thus to increase the

charging rate of capacitor C. When V

O2 is low, IF goes to

zero and the capacitor discharge current is set by I

The VC Lo-Pass Filter of

Figure 11 may be used to produce

a high-quality sinusoidal VCO. The circuit of

Figure 16 em-

ploys two LM13600 packages, with three of the amplifiers

configured as lo-pass filters and the fourth as a limiter/

inverter. The circuit oscillates at the frequency at which the

loop phase-shift is 360˚ or 180˚ for the inverter and 60˚ per

filter stage. This VCO operates from 5 Hz to 50 kHz with less

than 1% THD.

DS007980-21

FIGURE 14. Voltage Controlled State Variable Filter

LM13600 데이터시트(PDF) 13 Page - National Semiconductor (TI)