Question

The internal blocks in the Voltage-controlled-Oscillator (VCO) IC-566 are given below.
A. Current Sources,
B. Buffer Amplifier,
C. Schmitt Trigger,
D. Modulation Input.
Choose the correct sequence (input towards output) of internal blocks of VCO from the options given below from input side to output side:

• A. D, B, C, A
• B. D, C, B, A
• C. D, A, B, C
• D. D, A, C, B

Hint:

The core of most VCOs and function generators involves using a controllable current source to charge/discharge a capacitor, creating a triangle wave, which is then fed to a Schmitt trigger to create a square wave.

Answer 1

The Correct Option is D

Step 1: Understand the VCO's function. A Voltage-Controlled Oscillator (VCO) generates an output signal with a frequency controlled by an input voltage.
Step 2: Follow the signal flow in a typical VCO, such as the 566.

The process starts with the (D) Modulation Input voltage, which governs the frequency.
This voltage regulates internal (A) Current Sources, producing current proportional to the input voltage.
These sources alternately charge and discharge an external timing capacitor, causing the capacitor's voltage to ramp linearly up and down.
A (C) Schmitt Trigger monitors this voltage, switching its output when the capacitor voltage hits predefined upper and lower thresholds, generating a square wave.
The Schmitt trigger's output goes through a (B) Buffer Amplifier, providing a stable, low-impedance output signal.

Step 3: Construct the sequence. The correct signal sequence is D \(\to\) A \(\to\) C \(\to\) B.