Amplitude Modulation (AM) is one of the oldest and most widely used modulation techniques in communication systems. The basic concept behind AM is to modify the amplitude of a high-frequency carrier signal with the modulating signal, which typically contains the information to be transmitted. One of the key components of an AM system is the modulator, which generates the modulated signal from the modulating and carrier signals. In this blog post, we will focus on the generation of a standard AM signal using the AD633 analog multiplier IC
AD633 Analog Multiplier
The AD633 is a versatile analog multiplier IC that can be used in a variety of signal processing applications, including modulators. The AD633 is a four-quadrant multiplier, which means that it can handle both positive and negative input signals and produce both positive and negative output signals. The AD633 also has a wide input range and a high degree of linearity, which makes it ideal for modulator/demodulator applications. It is also used for multiplication, division, squaring, voltage controlled amplifier, attenuators and filters. Here it is illustrated how the AD633 IC for building AM modulator.
The AD633 integrated circuit pin out diagram is shown below.
Standard AM Signal Generation
To generate a standard AM signal using the AD633, we need to apply the modulating signal and the carrier signal to the inputs of the multiplier. The carrier signal is typically a high-frequency sine wave, and the modulating signal is the signal that contains the information to be transmitted. The output of the multiplier will be a signal that is proportional to the product of the modulating and carrier signals.
The amplitude of the modulating signal will determine the depth of modulation, which is the degree to which the carrier signal is modulated. The depth of modulation is typically expressed as a percentage, and a depth of modulation of 100% means that the carrier signal is completely modulated by the modulating signal.
The equation for a standard AM signal is:
\(s(t) = (1 + k_a m(t))A_c cos(2πf_ct)\)
where s(t) is the modulated standard AM signal, m(t) is the modulating signal, Ac and fc are the carrier amplitude and frequency, and ka is a constant that determines the depth of modulation.
The modulating signal or the message signal can be represented as,
\(m(t) = A_m cos(2πf_mt)\)
where, Am and fm are the message signal amplitude and frequency.
The mathematical behind the standard AM signal is explained with Matlab in the tutorial Standard AM signal in Matlab.
Standard AM with AD633 Circuit Diagram
To generate standard AM signal using the AD633, we can use the following circuit:
In this circuit, the message or modulating signal is applied to the X1 input of the AD633, and the carrier signal is applied to the Y1 input. The inputs X2 and Y2 are grounded. The FM signal appears at the product output pin W. The summing pin Z is grounded. The AD633 IC multiplier is operated using +5V and -5V. The resistor RL of 1KOhm is the load resistor.
Video demonstration
Conclusion
In this blog post, we have discussed the generation of a standard AM signal using the AD633 analog multiplier. The AD633 is a versatile IC(Integrated Circuit) that can be used in a variety of signal processing applications, including AM modulators. By applying the modulating and carrier signals to the inputs of the AD633, we can generate a modulated signal that is proportional to the product of the modulating and carrier signals. With the appropriate depth of modulation, we can transmit information using the modulated signal.
References:
[1] AM modulator using MC1496 modulator(Standard AM)
