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As the name implies, Pulse Amplitude Modulation (PAM) is an analogue modulation scheme in which the amplitude of the pulse carrier fluctuates in accordance with the current amplitude of the message signal. The amplitude of the original signal will be followed by the amplitude of the pulse amplitude modulated signal as the signal traces out the path of the entire wave. The reconstructed signal is sampled at the Nyquist rate and then passed through an efficient Low Pass Frequency (LPF) with an accurate cutoff frequency, which is known as natural PAM.
In the field of signal modulation, pulse-amplitude modulation (PAM) is a type of modulation in which the message information is encoded in the amplitude of a series of pulses. When the sample value of the message signal varies, the amplitudes of a train of carrier pulses are changed, resulting in an analogue pulse modulation method. Demodulation is accomplished by detecting the amplitude level of the carrier at each and every time period in the signal.
Types of PAMS
Pulse amplitude modulation are categorised into two types:
- To ensure that all of the pulses are positive in single polarity PAM, a preset DC bias is applied to the signal at a suitable fixed frequency.
- PAM with double polarity means that the pulses are both positive and negative at the same time.
When it comes to modifying signal transmission of digital data, pulse-amplitude modulation is commonly utilised, with non-baseband applications having been completely supplanted by pulse-code modulation and, more recently, by pulse-position modulation.
It is theoretically possible to have an endless number of different pulse amplitudes when using analogue PAM. The number of pulse amplitudes is reduced to a power of two when using digital PAM. Discrete pulse amplitudes are feasible in 4-level PAM, 8-level PAM, and 16-level PAM, for example.
It is possible to adjust the amplitude of each pulse using the instantaneous amplitude of a modulation signal, which is called pulse amplitude modulation (PAM). When the signal is sampled at regular intervals, a modulation system is created in which each sample is made proportional to the amplitude of the signal at the time of sampling. It sends data by encoding it in the amplitude of a series of signal pulses, which is done using this technology.
Because the carrier pulse train is modulated by a signal, the amplitude of each pulse varies in response to the modulating signal, with the amplitude of each pulse being determined by the value of m (t) at the time of the pulse transmission.
In reality, the pulses in a PAM signal can be of the Flat-top type, the natural type, or the ideal type. The PAM with a flat top is the most popular and commonly used. The reason for utilising Flat-top PAM during transmission is that during transmission, noise interferes with the top of the transmitted pulses, and this noise can be readily removed if the PAM pulse is designed as Flat-top PAM. In natural samples of the PAM signal, the pulse has a variable top in accordance with the variance in the signal. As soon as a pulse of this type is detected by the receiver, it is immediately tainted by noise. Then it becomes extremely difficult to distinguish the shape of the top of the pulse, and hence the amplitude detection of the pulse is not precise at this point.
Generation of PAM
There are two operations that take place during the creation of the PAM signal:
- Instantaneous sampling of the message signal m (t) every T(s) second, where the sampling rate fs = 1/T(s) is determined in accordance with the sampling theorem and the sampling rate fs = 1/T(s) is chosen in accordance with the sampling theorem
- Increasing the time of each sample until it reaches a certain constant value, such as T.
Pulse amplitude modulation is a technique in which the amplitudes of the pulses are modulated in response to the modulating signal. Pulse amplitude modulation is performed by multiplying the carrier with the modulating signal, which is denoted as m (t) in the diagram (t). As a result, the output consists of a series of pulses, the amplitudes of which fluctuate in response to the amount of modulating signal applied. This particular type of pulse amplitude modulation is referred to as natural PAM, and it is so named due to the fact that the tops of the pulses follow the shape of the modulating signal.
It serves as a periodic switching signal to the modulator, which when turned on allows samples of the modulating signal to be transmitted to the output. The sampling period is the amount of time that the pulse train repeats on a regular basis. It is important to note that T(s) is the time interval between the beginning of one sample and the beginning of the next, not the duration of the pulse.
Conclusion
It is possible to adjust the amplitude of each pulse using the instantaneous amplitude of a modulation signal, which is called pulse amplitude modulation (PAM). When the signal is sampled at regular intervals, a modulation system is created in which each sample is made proportional to the amplitude of the signal at the time of sampling. It sends data by encoding it in the amplitude of a series of signal pulses, which is done using this technology.
A PAM is created by combining a pure sine wave modulating signal with a square wave generator, which generates the carrier pulse, and a PAM modulator circuit, which generates the modulating signal. It is necessary to employ a sine wave generator that is based on the Wien Bridge Oscillator circuit. This has the potential to produce a sine wave with less distortion at the output. An amplitude and frequency adjustment potentiometer are used in this circuit to allow users to fine-tune the oscillator’s amplitude and frequency.
