How to convert analogue signals to digital signals?
Posted on Dec 29, 2008 under Digital news and reports |Please answer according to A - level Physics syllabus.
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Please answer according to A - level Physics syllabus.
December 29th, 2008 at 7:17 am
You define a threshold A and a sampling rate f (Hz).
Every 1/f seconds you read the analogue signal; if the strength is greater than A then it's a 1, otherwise a 0.
December 29th, 2008 at 7:17 am
"digitize it".
measure the signal amplitude as a function of time (in small periods of equal length).
with the analog signal measured in that time interval, you've converted the amplitude into a number. now, just convert that number into binary and send the bits over a ribbon cable.
what you are asking about is also called a "modem". computers used to use these to send/receive digital data over analog transmission lines…
cheers
December 29th, 2008 at 7:17 am
if you sent analogue signals in to amplifier then you get digital signal.
December 29th, 2008 at 7:17 am
I don't know what A-level is, but I hope it expects more knowledge than the 3 preceding answers have given.
To summarize the A-D converter's function, it generates a digital number that is proportional to an input signal voltage. This enables computers and other digital equipment to process and act on real-world data obtained from analog devices.
An A-D converter contains a comparator and a D-A converter.
The D-A converter produces an analog voltage proportional to the binary (digital) number it is given. Each bit in the binary number switches in (adds) a resistor to a network of precision resistors connected to a precision reference voltage source. The network output is the reference voltage * the binary number (scaled from 0 to 1).
This output is fed to input A of the comparator, which compares two analog voltages A and B and switches off if A >= B, otherwise on. The input analog signal to be converted is connected to comparator input B.
Now the output of a binary counter (counting from 0 to 1 scale in small steps) is fed to the D-A converter, which produces a voltage ramp at A. When A >= B, the comparator switches off and the counter stops. The value in the counter is the binary representation of the signal voltage, and that value is the output of the A-D converter.
Actually there are smarter, faster ways to reach the correct binary value than counting up from zero. A smarter converter does it one bit at a time, requiring only, say, 16 steps of D-A conversion and comparison instead of 2^16 = 64000 steps (for a 16-bit converter). The most significant bit, representing 1/2 of full scale, is first applied. If the comparator says it's too high it's removed, otherwise it stays. Next the 1/4 scale bit is tested, and so forth down to the last bit (1/64000 scale). The states of all 16 bits are saved in a register, which provides the A-D output. Fast versions of these converters can operate at up to multi-MHz speeds.
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