Numerical on VCO Connection
Q. For the circuit shown below, +V = 15V, R2 = 1K, R1 = R3 = 8K & C1 = 0.001μF. Compute
(a) nominal frequency of output waveforms &
(b) Modulation in the output frequencies if Vc changes in the mist of 10V to 11.5V.
- Published on 26 Oct 15a. 26.17 & 33.34 kHz
b. 35.60 kHz & 10 kHz
c. 30.47 kHz & 10 kHz
d. 22.56 & 33.34 kHz
ANSWER: 30.47 kHz & 10 kHz
(a) By applying voltage -divider rule, initial voltage at terminal 5 is given by,
Vc = (20K) (15) / 11.5K = 26.09 V
Thus, the frequency of output waveform (nominal frequency) is approximated by,
fo ≈ 2(+V - Vc) / R1C1 (+V)
= 2 (15 – 10.43) / (20K x 10-9) x (15)
= 30.47 kHz
(b) Thus, the modulation in the output frequencies can be calculated by initially substituting Vc = 10V & then 11.5 V
fo = 2 (15 – 10) / 20K x 10-9 x 15
= 33.34 kHz
fo = 2 (15 – 11.5) / 20K x 10-9 x 15
= 23.34 kHz
Hence, the variation in an output frequency can be evaluated by the difference between these both frequencies.
i.e. 33.34 - 23.34 = 10 kHz.
