Modulator vs. Multiplier: Key Differences Explained

This article compares Modulators and Multipliers, highlighting their key differences. It also provides equations and examples for both.

Modulator

A modulator is a circuit that modifies one input signal based on another. Typically, it has at least two inputs.

Figure 1: Typical Modulator Operation

As shown in Figure 1, fA and fB are arbitrary functions of the input signals v1(t) and v2(t) respectively. The modulator uses one signal to control or modify the other.

Example:

Let’s say the modulated signal (Vm) is represented as:

$Vm = Am * Cos(2 * π * fm * t)$

And the carrier signal (Vc) is represented as:

$Vc = Ac * Cos(2 * π * fc * t + Φ)$

In the modulated output:

• For Amplitude Modulation (AM), Ac varies according to the amplitude of the modulating input signal.
• For Frequency Modulation (FM), fc varies according to the frequency of the modulating input signal.
• For Phase Modulation (PM), Φ varies according to the phase of the modulating input signal.

Multiplier

Figure 2: Typical Multiplier Operation

Figure 2 depicts the operation of a typical Multiplier. Similar to a modulator, it also takes multiple inputs. In this case, fA and fB are linear functions of v1(t) and v2(t) respectively.

Multipliers find use in nonlinear analog signal processing, mixing, frequency translation, modulation, and demodulation, among other applications.

Types of Multipliers:

• One Quadrant multiplier
• Two Quadrant multiplier
• Four Quadrant multiplier

Applications of Multipliers:

• Frequency doubling
• Positive and negative division
• Square root operation
• Cube root operation

Key Differences Summarized

While both modulators and multipliers process multiple input signals, the key difference lies in the function applied to the inputs:

• Modulator: At least one of the functions fA or fB applied to the input signals is a non-linear function. Modulation aims to encode information onto a carrier signal.
• Multiplier: Both functions fA and fB are linear functions. Multipliers perform a direct multiplication of the input signals.