Analog to digital converter and multi vibrators
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Analog-to-Digital Converter and Multi-vibrators. Simple Digital to Analog Converter. .111 corresponds to 7/8 7/8 of 5 is 4.375. Simple Digital to Analog Converter. .100 corresponds to 1/2 1/2 of 5 is 2.5. Analog-to-Digital.

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Analog-to-Digital Converter and Multi-vibrators

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Analog to digital converter and multi vibrators

Analog-to-Digital Converter and Multi-vibrators


Simple digital to analog converter

Simple Digital to Analog Converter

.111 corresponds to 7/8

7/8 of 5 is 4.375


Simple digital to analog converter1

Simple Digital to Analog Converter

.100 corresponds to 1/2

1/2 of 5 is 2.5


Analog to digital

Analog-to-Digital

  • We have seen a simple digital-to-analog converter, now we consider the reverse process

  • For this purpose we introduce a new circuit element — the comparator

  • We have seen last semester a digital comparator, a logic circuit that determined whether the input word A is larger than the input word B

  • Now we look at an analog comparator, it determines whether voltage A is larger than voltage B


Comparator analog

Comparator (analog)

+ Input higher than – input, output is high


Comparator analog1

Comparator (analog)

+ Input lower than – input, output is low


1 bit analog digital converter

1-bit analog-digital converter

Input voltage is less than half of reference voltage, result is low.

Reference Voltage

Input voltage


1 bit analog digital converter1

1-bit analog-digital converter

Input voltage is more than half of reference voltage, result is high.

Reference Voltage

Input voltage


Toward a 2 bit analog digital converter

Toward a 2-bit analog-digital converter


Toward a 2 bit analog digital converter1

Toward a 2-bit analog-digital converter


Toward a 2 bit analog digital converter2

Toward a 2-bit analog-digital converter


Toward a 2 bit analog digital converter3

Toward a 2-bit analog-digital converter


Finish this truth table

Finish this truth table

Doesn’t occur


Integrated circuit version

Integrated circuit version

Warning: may need to flip switch back and forth.


3 7 5 in scientific mode

3.7 / 5 (in Scientific Mode)


Binary mode

Binary Mode


Compare

Compare


Scientific mode

Scientific Mode


Multi vibrators

Multi-vibrators

http://www.ee.ed.ac.uk/~kap/Hard/555/node1.html


Multi vibrator

Multi-vibrator

  • A multi-vibrator is an electronic circuit that can exist in a number of “states” (voltage and/or current outputs).

  • A flip-flop is a bi-stable multi-vibrator, bi-stable means it has two stable states.

  • A state is stable if it is robust against the fluctuations (noise) that are always occurring.


Mono stable multi vibrator

Mono-stable multi-vibrator

  • A mono-stable multi-vibrator has one stable output (usually zero).

  • It also has an unstable state. Certain input will put the circuit into its unstable state, which lasts for a set length of time before returning to the stable state.

    • Unstable states are still robust to noise but do not last indefinitely long.

  • In wave terminology, this provides one with a single pulse.


Pulse

Pulse

STABLE

STABLE

UNSTABLE


One shots

One shots

  • One purpose of a mono-stable multi-vibrator is to output a signal of a specified duration.

  • The input (trigger) may be short (or unknown) in duration, but the output pulse has a predictable duration (can be controlled by the time constant of an RC circuit).

    •  = RC

    • The time constant and duration are not equal but are proportional.

  • Such a circuit is called a “one shot.”


Shapers

Shapers

  • Another purpose of mono-stable multi-vibrators is to “shape” input signals.

  • Recall in digital circuits we want signals to be clearly high or low; a mono-stable multi-vibrator can take signals which are not of this form and create signals which are.


Schmitt trigger

Schmitt trigger


Schmitt trigger1

Schmitt trigger

  • If the voltage is above a certain value (the upper trip point) and rising, the output is high.

  • If the voltage is below another value (the lower trip point) and falling, the output is low.

  • Otherwise, it remains whatever it was.


Schmitt trigger2

Schmitt trigger

The upper trip point

Above the upper trip and going up

Below the lower trip and going down

The lower trip point


A stable multi vibrator

A-stable multi-vibrator

  • In an a-stable multi-vibrator, there are typically two states, neither of which is stable.

  • The circuit repeatedly flips back and forth between the states.


A stable multi vibrator1

A-stable multi-vibrator


A stable multi vibrator2

A-stable Multi-vibrator

  • Assume a state where the transistor on left is ON and transistor on right is OFF and the capacitor on the left has no charge.

  • Since the left transistor is on (hard) it is not dropping much voltage, therefore “all” the voltage is being dropped by the resistors

  • The capacitor on the left begins to charge through the 10K resistor on the right


A stable multi vibrator3

A-stable Multi-vibrator


A stable multi vibrator oscilloscope

A-stable Multi-vibrator Oscilloscope


A stable

A-stable

high

low

OFF

ON

Charge building up


A stable1

A-stable

  • Charge builds up on the left capacitor, “pulling-up” the voltage presented to the base of the transistor on the right.

  • When the base reaches about 0.7v the transistor on the right turns on.

  • Current now starts to flow through the 1K resistor on the far right, thus dropping the voltage level at the collector.

  • That low voltage makes its way to the base of the transistor on the left turning it off.

  • The cycle repeats itself.


A stable2

A-stable

low

ON

Turns off


Duty cycle

Duty cycle

  • In a square wave (e.g. a computer’s clock), the wave is characterized by its frequency, its amplitude and its duty cycle.

  • The duty cycle is the percent of time that the signal is high.

  • Duty cycle = thigh/(thigh+tlow)*100%


Duty cycle example t high 1 407 ms

Duty cycle example: thigh = 1.407 ms


Duty cycle example t high t low 2 111 ms duty cycle 1 407 2 111 66 65

Duty cycle example: thigh + tlow = 2.111 msDuty cycle = (1.407/2.111) = 66.65%


555 timer

555 Timer

  • A similar circuit uses the 555 chip (Integrated circuit)

  • The resistors and capacitors are external to the chip so that the period and duty cycle of the circuit can be controlled.


Analog to digital converter and multi vibrators

555


555 as monostable multivibrator

555 as Monostable multivibrator


555 as astable multivibrator

555 as Astable Multivibrator


555 timer workbench version

555 Timer (WorkBench version)


Crystals

Crystals

  • The very high frequency square wave used for the CPU clocks are not generated in the manner described on the previous slides.

  • The high frequency signal is supplied by crystals subjected to an electric field.


References

References

  • http://www.ee.ed.ac.uk/~kap/Hard/555/node2.html#modes

  • http://en.wikipedia.org/wiki/555_timer_IC

  • http://www.kpsec.freeuk.com/555timer.htm


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