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Waveform converter circuits-convert one type of wave into other

There are many different kind of waveforms like sine wave, cosine wave, square wave, triangular wave, sawtooth wave, pulses, spikes, stair-case wave, ramp etc. All these waveforms are generated using oscillator circuits. And basically there are three types of oscillators only Sine wave oscillator Square wave oscillator Pulse generator Then how other types of waveforms can be generated? The answer is waveform converter circuits. Such circuits convert one type of wave into other. The function generator itself uses such circuits to generate different kinds of waveforms.

Step 1: Required factors

These circuits are very much useful when some circuits require one specific kind of wave as an input. For example

· The input to VCO (voltage controlled oscillator) is sawtooth wave only

· The input to any digital (CMOS or TTL) circuit is pulses only

So here I have presented 3 of such circuits that convert one type of wave into another. These circuits can be easily build on general purpose PCB or even on bread board using very few components and can be tested using general laboratory instruments.

So let us first collect the required components and instruments to build and test these circuits

Required Instruments:

· Dual power supply

· Function generator

· DSO (or CRO)

Required Components:

· IC LM741 – operational amplifier

· Resistor – 4700 ?

· Capacitor – 0.01 µF

Along with these components and instruments, you require following apparatus also

Required Apparatus:

· Bread board – to mount component

· Connecting wires – to connect component

· CRO probes – to connect input and output of circuit with function generator and CRO

Now let us start with very simple circuit that converts sine wave into square wave

Step 2: Circuit description:

· Sine wave input is applied at inverting terminal (2)

· Non inverting terminal (3) is grounded

· Square wave output is taken from output terminal (6)

· +5 V supply is given to +Vcc terminal (7) and -5 V supply is given to –Vee terminal (4)

Now have a look at how the above circuit works.

Step 3: Circuit operation:

When IC LM741 is connected in comparator mode it converts sine wave into square wave of same frequency. The sine wave input is applied at inverting terminal of chip and non inverting terminal is grounded. So IC741 compares input on inverting terminal with 0 V. During positive cycle the input at inverting terminal is more than non inverting terminal so the output of chip will be +Vcc. While during negative cycle the input at inverting terminal is less than non inverting terminal so the output of chip will be –Vcc. Thus the output swings from +Vcc to –Vcc and so on as sine wave input cycle changes.

· A sine wave of around 1 KHz with at least 2 Vpp (-1 V to +1 V) is applied at the input

· In positive cycle of input, as it crosses 0 V mark, the voltage at inverting terminal is more than non inverting terminal. So output switches to -5 V

· Similarly in negative cycle of input, as it crosses 0 V mark, the voltage at inverting terminal becomes less than non inverting terminal. So output switches to +5 V.

· Thus output swings from +5 V to – 5 V and -5 V to +5 V as input sine wave crosses 0 mark

· So the frequency of input sine wave and output square wave are same.

Now after understanding the circuit operation and building the circuit on bread board next is to test the circuit. So follow the step by step procedure to test the circuit

Step 4: Test Procedure:

Set 4 Vpp @ 1 KHz sine wave in function generator by connecting its output directly to 1^st channel of DSO using CRO probes
Apply this sine wave to the input of circuit
Connect the output of the circuit to 2^nd channel of DSO using CRO probe
Connect +5 V, - 5V and ground to the circuit from dual power supply
Switch on power supply
Observe input and output waveforms on DSO

Here is the photograph of test setup of circuit.

When you follow above step by step procedure you will get output on CRO (DSO) as per given photograph.

In above photograph sine wave in yellow colour is an input to circuit applied to 1^st channel of DSO and square wave in blue colour is an output from circuit applied to 2^nd channel of DSO

You would be wondering where this circuit can be used?

The answer is, this circuit can be used where it is required that input should have only two states either positive or negative. Also by applying some reference voltage at non inverting terminal the circuit can generate PWM wave whose pulse width can be varied by varying reference voltage.

Now let’s move ahead with next circuit that converts square wave into triangle wave.