Pulse Amplitude Modulation Circuit Pdf FileIntroduction to Pulse Width Modulation. A look at a powerful technique for controlling analog circuits with a microprocessor's digital outputs. PWM is employed in a wide variety of applications, ranging from measurement and communications to power control and conversion. A nine- volt battery is an example of an analog device, in that its output voltage is not precisely 9. V, changes over time, and can take any real- numbered value. Similarly, the amount of current drawn from a battery is not limited to a finite set of possible values. Analog signals are distinguishable from digital signals because the latter always take values only from a finite set of predetermined possibilities, such as the set . In a simple analog radio, a knob is connected to a variable resistor. As you turn the knob, the resistance goes up or down. As that happens, the current flowing through the resistor increases or decreases. This changes the amount of current driving the speakers, thus increasing or decreasing the volume. An analog circuit is one, like the radio, whose output is linearly proportional to its input. For one thing, analog circuits tend to drift over time and can, therefore, be very difficult to tune. Precision analog circuits, which solve that problem, can be very large, heavy (just think of older home stereo equipment), and expensive. Analog circuits can also get very hot; the power dissipated is proportional to the voltage across the active elements multiplied by the current through them. ![]() ![]() Pulse amplitude modulation using pspice datasheet, cross reference, circuit and application notes in pdf format. Modulation and Demodulation Trainer ST2110 Learning Material. Pulse Amplitude Modulation 18 VI. Sample and Hold Circuit 21 VII. Pulse Position Modulation 25 VIII. Pulse Width Modulation 25. The simple pulse modulation technique called Pulse Amplitude Modulation. Circuit Design: Pulse Amplitude Demodulation.
Analog circuitry can also be sensitive to noise. Because of its infinite resolution, any perturbation or noise on an analog signal necessarily changes the current value. What's more, many microcontrollers and DSPs already include on- chip PWM controllers, making implementation easy. Through the use of high- resolution counters, the duty cycle of a square wave is modulated to encode a specific analog signal level. The PWM signal is still digital because, at any given instant of time, the full DC supply is either fully on or fully off. The voltage or current source is supplied to the analog load by means of a repeating series of on and off pulses. The on- time is the time during which the DC supply is applied to the load, and the off- time is the period during which that supply is switched off. Given a sufficient bandwidth, any analog value can be encoded with PWM. Figure 1a shows a PWM output at a 1. That is, the signal is on for 1. Figures 1b and 1c show PWM outputs at 5. These three PWM outputs encode three different analog signal values, at 1. If, for example, the supply is 9. V and the duty cycle is 1. V analog signal results. In the figure, a 9. V battery powers an incandescent lightbulb. If we closed the switch connecting the battery and lamp for 5. V during that interval. If we then opened the switch for the next 5. V. If we repeat this cycle 1. V battery (5. 0% of 9. V). We say that the duty cycle is 5. Hz. Imagine that our lamp was switched on for five seconds, then off for five seconds, then on again. The duty cycle would still be 5. In order for the bulb to see a voltage of 4. To achieve the desired effect of a dimmer (but always lit) lamp, it is necessary to increase the modulating frequency. The same is true in other applications of PWM. Common modulating frequencies range from 1k. Hz to 2. 00k. Hz. For example, Microchip's PIC1. C6. 7 includes two, each of which has a selectable on- time and period. The duty cycle is the ratio of the on- time to the period; the modulating frequency is the inverse of the period. To start PWM operation, the data sheet suggests the software should. Set the period in the on- chip timer/counter that provides the modulating square wave. By keeping the signal digital, noise effects are minimized. Noise can only affect a digital signal if it is strong enough to change a logical- 1 to a logical- 0, or vice versa. Switching from an analog signal to PWM can increase the length of a communications channel dramatically. At the receiving end, a suitable RC (resistor- capacitor) or LC (inductor- capacitor) network can remove the modulating high frequency square wave and return the signal to analog form. As a concrete example, consider a PWM- controlled brake. To put it simply, a brake is a device that clamps down hard on something. In many brakes, the amount of clamping pressure (or stopping power) is controlled with an analog input signal. The more voltage or current that's applied to the brake, the more pressure the brake will exert. To produce more stopping power, the software need only increase the duty cycle of the PWM output. If a specific amount of braking pressure is desired, measurements would need to be taken to determine the mathematical relationship between duty cycle and pressure. It would then set the PWM duty cycle to the new value and the brake would respond accordingly. If a sensor is available in the system, the duty cycle can be tweaked, under closed- loop control, until the desired pressure is precisely achieved. And it's now in your bag of tricks. He is also the author of Programming Embedded Systems in C and C++ (O'Reilly, 1. University of Maryland.
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