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To Know

posted Mar 25, 2012, 6:50 PM by Neil Mathew   [ updated Apr 11, 2012, 8:13 AM ]
In electronics, a sample and hold (S/H, also "follow-and-hold"[1]) circuit is an analog device that samples (captures, grabs) the voltage of a continuously varying analog signal and holds (locks, freezes) its value at a constant level for a specified minimal period of time. Sample and hold circuits and related peak detectors are the elementary analog memory devices. They are typically used in analog-to-digital converters to eliminate variations in input signal that can corrupt the conversion process.

A typical sample and hold circuit stores electric charge in a capacitor and contains at least one fast FET switch and at least oneoperational amplifier.[1] To sample the input signal the switch connects the capacitor to the output of a buffer amplifier. The buffer amplifier charges or discharges the capacitor so that the voltage across the capacitor is practically equal, or proportional to, input voltage. In hold mode the switch disconnects the capacitor from the buffer.

high-pass filter (HPF) is an electronic filter that passes high-frequency signals but attenuates (reduces the amplitude of) signals with frequencies lower than the cutoff frequency.

low-pass filter is an electronic filter that passes low-frequency signals but attenuates (reduces the amplitude of) signals with frequencies higher than the cutoff frequency

A buffer amplifier, or simply a buffer, is an electronic amplifier that is designed to have an amplifier gain of 1. Buffers are used in Impedance matching, the benefit of which is to maximize energy transfer between circuits or systems.

There are two main kinds of buffer circuits, Voltage buffers and Current buffers. The purposes of each is to isolate the mentioned characteristic to avoid loading the input circuit or source from the output stage.

An encoder is a device, circuit, transducer, software program, algorithm or person that converts information from one format or code to another, for the purposes of standardization, speed, secrecy, security, or saving space by shrinking size.
(PCM= takes the anlog signal and converts it into a 8bit or 4bit binary code._

serial communication is the process of sending data one bit at a time, sequentially, over a communication channel or computer bus. This is in contrast to parallel communication, where several bits are sent as a whole, on a link with several parallel channels. 

parallel communication is a method of sending several data signals simultaneously over several parallel channels. It contrasts with serial communication; this distinction is one way of characterizing a communications link.

- What is the difference between bipolar and unipolar devices ?Bipolar transistors can have both minority and majority carriers flowing, whereas FET's only have majority carriers flowing. The fact that bipolar transistors have two types of carriers flowing simultaneously results in the name 'bi-polar'. The monirity carrier flow is responsible for collector conduction modulation and transistor storage time.

Ma'am explained the difference between unipolar and bipolar as two types of waveforms.

unipolar being the 1 0 type wave. (digital)
and bipolar being the sine wave (analog, continuous)

Below Diagram explains it ALL:


Each sample of the analog signal is encoded into a code (4 bit example in this case) which can be seen below:


 shows a delta-modulation encoder; it is known as a single integration modulator. 

The input signal is compared to the integrated output pulses and the delta (difference) signal is applied to the quantizer. 

The quantizer generates a positive pulse when the difference signal is negative, and a negative pulse when the difference signal is positive. 

This difference signal moves the integrator step by step closer to the present value input, tracking the derivative of the input signal.