ECE Projects
 
 

 

Electronic Projects

       AudioRF Circuits 
     
      Event Detection Circuits 
         
      Math Function Circuits 
         
      Measurement Circuits 
    
      Motor Control Circuits 
         
      Power Supply Circuits 
         
      Sensing Circuits 
         
      Special Function Circuits 
         
      Switching Circuits 
     
      Timing Circuits 
         
      ToneWave Generators

Quadrature Oscillator Circuit

Figure 1.  A Quadrature Oscillator Using Two Op-Amps

Figure 1 shows a quadrature oscillator that uses two op-amps. A quadrature oscillator is a circuit that generates two periodic signals that are in quadrature, i.e., they are 90 degrees out of phase.

The circuit in Figure 1 generates a sine wave and a cosine wave, which were arbitrarily taken from the outputs of operational amplifiers A1 and A2, respectively. This circuit basically consists of two parts: an amplifier circuit consisting of A1 and A2 and a feedback circuit composed of Rf and Cf. 

A feedback amplifier circuit such as this oscillates because it satisfies the two basic requirements for oscillation: 1) the total phase shift around the amplifier-feedback loop is 0 or 360 degrees; and 2) the magnitude of the loop gain must be at least equal to 1. A1 is configured as a non-inverting integrator whose input is taken from the output of A2 through the Rf-Cf feedback circuit.  A2 is configured as a pure integrator that converts the sine wave output of A1 into its cosine output.

Note that this circuit satisfies the conditions for oscillation only at a single frequency fo, which is given by: fo = 1 / (2pRC) where RC = R1C1 = R2C2 = RfCf.