- We Are Going To Investigate A Circuit Known As A Voltage Controlled Oscillator This Particular Implementation Generates 1 (31.52 KiB) Viewed 16 times
- We Are Going To Investigate A Circuit Known As A Voltage Controlled Oscillator This Particular Implementation Generates 2 (41.8 KiB) Viewed 16 times
- We Are Going To Investigate A Circuit Known As A Voltage Controlled Oscillator This Particular Implementation Generates 3 (29.15 KiB) Viewed 16 times
function of the integrator components R and C, the power supply
voltage Vcc, and the input voltage Vin.
We are going to investigate a circuit known as a Voltage Controlled Oscillator. This particular implementation generates a triangle wave at one output, whose frequency of oscillation is controlled by a DC voltage input. The basic components of this VCO are a polarity controlled integrator, and an inverting Schmitt Trigger. For this implementation of the ST, we will use be using an Op-Amp (with positive feedback). The output of the integrator is the input to the ST. The output of the ST is connected to the Gate of a NFET, which controls the polarity of integration. Toggling this switch changes the polarity of the integrator constant from negative to positive, or vice versa.
The rate of the ramp function on the integrator is a function of the integrator feedback capacitor, the integrator resistors, and the DC voltage input. The higher the input DC voltage, the faster the integrator output voltage ramps up, thus producing a higher frequency of oscillation. The integrator output voltage will ramp until we hit the switching voltage for the ST, which will toggle the polarity of the ramp, and then the integrator will begin to ramp down, unitl it hits the lower ST switching voltage, and the process repeats. The frequency of oscillation as a function of the integrator components (R. C) and the input voltage, assuming an ideal OpAmp and #Ver power supplies, is approximately: 1 f Ving-R-C-VCC (Hz) Eq. 1 Practically, the frequency of oscillation will be slightly higher than the formula predicts. With R=1k, C=1uF, and Vcc= 12V, equation 1 reduces to : f 10.42. Vin (Hz) Eq.2
C1 HH 1u Vee R1 =2R 4 2 2k V- ua741 081 triangle R3=R 6 V+ 6 Vin 3 U1 Vcc 1k OH 1k R4 =R Vcc V1 12 Vee R2 =R 1k V2 4 M1 12 V- squares 6 M2n7000 OG1 ua741 V+ + 3 7 14 ' 5 Vee Vcc R5 100K R5=R6 100k R6