* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Analog-to-Digital Converter and Multivibrators
Ground loop (electricity) wikipedia , lookup
Time-to-digital converter wikipedia , lookup
Three-phase electric power wikipedia , lookup
Spark-gap transmitter wikipedia , lookup
Flip-flop (electronics) wikipedia , lookup
History of electric power transmission wikipedia , lookup
Immunity-aware programming wikipedia , lookup
Electrical ballast wikipedia , lookup
Variable-frequency drive wikipedia , lookup
Power inverter wikipedia , lookup
Electrical substation wikipedia , lookup
Two-port network wikipedia , lookup
Regenerative circuit wikipedia , lookup
Current source wikipedia , lookup
Pulse-width modulation wikipedia , lookup
Surge protector wikipedia , lookup
Alternating current wikipedia , lookup
Stray voltage wikipedia , lookup
Power MOSFET wikipedia , lookup
Oscilloscope history wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Analog-to-digital converter wikipedia , lookup
Power electronics wikipedia , lookup
Voltage optimisation wikipedia , lookup
Voltage regulator wikipedia , lookup
Integrating ADC wikipedia , lookup
Mains electricity wikipedia , lookup
Current mirror wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Schmitt trigger wikipedia , lookup
Analog-to-Digital Converter and Multi-vibrators 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 considered 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) Almost what we want • What we want: if the voltage into – input exceeds the voltage into the + input, then the output is low; otherwise it is high • What we have: if the voltage into – input exceeds the voltage into + input by 0.7, then the output is low; otherwise it is high 1-bit analog-digital converter Voltage here is half reference voltage of 5 volts That extra 0.7 volts 1-bit analog-digital converter Toward a 2-bit analog-digital converter 3/4 1/2 1/4 Toward a 2-bit analog-digital converter Toward a 2-bit analog-digital converter Toward a 2-bit analog-digital converter Integrated circuit version Multi-vibrators http://www.ee.ed.ac.uk/~kap/Hard/555/node1.html 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, bistable 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 • 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 • In wave terminology, this provides one with a single pulse. Pulse STABLE UNSTABLE STABLE 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 • Another purpose of mono-stable multivibrators is to “shape” input signals. • Recall in digital circuits we want signals to be clearly high or low; a mono-stable multivibrator can take signals which are not of this form and create signals which are. Schmitt trigger 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 trigger The upper trip point Above the upper trip and going up The lower trip point Below the lower trip and going down 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-vibrator 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 high low ON OFF Charge building up A-stable • Charge builds up on the left capacitor, “pullingup” 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-stable low Turns off ON 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% 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. 555 555 as Monostable multivibrator 555 as Astable Multivibrator 555 Timer (WorkBench version) 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.