Using pulse width modulation with carrier frequency changing for transmission of two separate signals
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Using pulse width modulation with carrier frequency changing for transmission of two separate signals Milan Stork1 Received: 13 February 2020 / Revised: 15 October 2020 / Accepted: 22 October 2020 Ó Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Pulse width modulation (PWM) is widely used in different applications. PWM transforms the information in the amplitude of a bounded input signal into the pulse width output signal without suffering from quantization noise. The frequency of the output signal is usually constant. In this paper, the new PWM system with frequency changing (PWMFM) is described. In such PWMFM the pulse width and also the carrier frequency are changed. Therefore, two independent pieces of information can be simultaneously transmitted over one channel; hence PWM and frequency modulation (FM) are simultaneously used. But such system needs 2 demodulators, one for PWM and the second for FM. PWMFM can be used in the following applications: LED light intensity control via PWM and several LED block switching by FM PWMFM is highly useful in motor speed control applications by PWM and direction of rotation with FM. PWMFM can be used also in a class-D audio amplifier for power control, e.g. coarse by means of FM and fine by PWM. PWMFM can be used for the simultaneous transmission of two independent information between all, mutual combinations of analog and digital circuits. The analog and digital circuits for modulation and demodulation of PWMF signal are described and measuring results are presented in this work. Keywords Pulse width modulation Frequency modulation Pulse width demodulation Frequency to voltage converter Phase locked loop
1 Introduction PWM, or pulse-duration modulation (PDM), is a technique used to encode a message into a pulsing signal. It is a type of modulation and therefore this modulation technique can be used to encode information for transmission. Pulsewidth modulation uses a rectangular pulse wave whose width is modulated, resulting in the variation of the average value of the waveform. PWM can take different forms [1–8]. A constant-frequency PWM signal can be produced simply by comparing a reference signal x(t), with a carrier signal c(t). Simple principle of analog version is shown in Fig. 1. For the demodulation of the PWM signal the classical concept employs a low pass filter of different order. Some applications are listed in [9–14]. For the FM & Milan Stork [email protected] 1
demodulation it is also possible to use different circuits but monostable multivibrator with low-pass filter is the simplest. The digital PWM output can be mathematically written as yPWM ¼ sign½xðtÞ cðtÞ
ð1Þ
where x(t) is input signal, c(t) is carrier signal and sign(x) = 1 if x [ 0, 0 if x = 0 and - 1 if x \ 0. The digital PWM signal can be generated by microcontroller (lC) by means of counters, see Fig. 2, where period T is fixed and width W is changing. Now, almost all lCs have capabilities to generate PWM. In this paper the PWM with variable frequency modu
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