Many electronic devices depend upon the shape of the signals. It is very easy to produce
squarewave signals from sine wave, but reproducing sinewave signals from the square wave is quite difficult.

In case of static squarewave-to-sinewave converter, in low frequency range, we can get accurate sine wave, but in high frequency range the shape will not be a true sine wave. Here is a solution to that problem.

The circuit shown here uses five ICs. The squarewave signal is fed at pin 1 of IC1 (CD 4024). IC1 is a 7-bit counter, but here only 6 bits are made use of. The first four bits are fed as a signal bus to IC3 (CD4066) quad bilateral switch through IC2 (CD4077B) that contains four exclusive NOR gates.

It converts the 4-bit signal bus to ‘up mode’ and ‘down mode’ hexadecimal signals, simultaneously. The converted signal bus switches on and off the ladder switches inside CD4066. As a result, the net resistance of ladder varies.

This varying resistance varies the charging and discharging current of capacitor C1 in the feedback path of IC5 (LM741). The charging and discharging mode is controlled by IC4 (CD4011). In fact, capacitor C1 works as an integrator.

The sinewave producing circuit needs 64- bit squarewave pulse for360o sine wave. A missing pulse in this 64-bit sequence produces ramp. In this circuit, all ICs except IC5 are CMOS ICs and hence the current consumption is very low.

The value of capacitor C1 may be calculated from the relationship: C1 = 0.27/f0 μF. The value shown in the circuit is for 50Hz output frequency. The shape of the sinewave output may be corrected using presets VR1 and VR2.

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