1 / 21

310 likes | 1.35k Vues

Analog to Digital Conversion. Introduction. An analog-to-digital converter ( ADC , A/D , or A to D ) is a device that converts continuous signals to discrete digital numbers

Télécharger la présentation
## Analog to Digital Conversion

**An Image/Link below is provided (as is) to download presentation**
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.
Content is provided to you AS IS for your information and personal use only.
Download presentation by click this link.
While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

**Introduction**• An analog-to-digital converter(ADC, A/D, or A to D) is a device that converts continuous signals to discrete digital numbers • In electronics, a digital-to-analog converter(DAC or D-to-A) is a device for converting a digital (usually binary) code to an analog signal (current, voltage or charges). Digital-to-Analog Converters are the interface between the abstract digital world and the analog real life. Simple switches, a network of resistors, current sources or capacitors may implement this conversion**Important terminologies in ADC**• Resolution • Response type • Linear ADCs • Non-linear ADCs • Accuracy • Sampling rate • Aliasing**Resolution**• The resolution of the converter indicates the smallest analog value that it can convert to a digital number • If the ADC has 8 bits and the Full scale is 0-5 Volts, then the ADC voltage resolution is: • 5/28 = 0.01953125 Volts**Response type**• Linear ADCs • Output binary value changes approximately with the analog value within the resolution (or ½ the resolution) • Non-linear ADCs • Uses techniques known as companding to ‘magnify” the low amplitude analog signals • m-law • A-law • Dolby**Accuracy**• Accuracy depends on • Quantization error • Non-linear error caused by the physical imperfections of ADC**Sampling rate**• For ADC, a signal values are measured and stored at intervals of time Ts, the sampling time. • A bandlimited analog signal must be sampled at a frequency fs = 1/Ts that is twice the maximum frequency (fa) of the bandlimited signal • fs = 2fa is known as the Nyquist Sampling frequency**Aliasing**• If a signal values are measured and stored at frequencies greater than the Nyquist sampling rate, the signal can be reproduced exactly (within quantization and other non-linear error accuracy). • However, If a function is sampled at less than Nyquist rate, the resulting function may have different frequency content. This is known as aliasing. • For example: If a 3 KHz sine wave is sampled at 4 KHz, the resulting signal will appear as a 1 KHz signal.**How is it doneDigital-Ramp ADC**http://hyperphysics.phy-astr.gsu.edu/HBASE/Electronic/adc.html**How is it doneSuccessive Approximation ADC**http://hyperphysics.phy-astr.gsu.edu/HBASE/Electronic/adc.html**How is it doneFlash ADC**http://hyperphysics.phy-astr.gsu.edu/HBASE/Electronic/adc.html**Analog to Digital chip: ADC0820**• 8-Bit High Speed µP Compatible A/D Converter with Track/Hold Function • Uses ½ flash conversion technique • consists of 32 comparators • a most significant 4-bit ADC • a least significant 4-bit ADC • 1.5 µs conversion time • Does not need external sample-and-hold for signals moving at less than 100 mV/µs.**Analog to Digital chip: ADC0820**• Has many input modes, RD, WR-RD, WR-RD Standalone • Input pulse required to read analog data (Sample) • Must sample at more than Nyquist rate (fs = 2*fa) • Outputs signal when data is valid**ADC0820 – WD-RD Mode**t1 = tINTL= 800 ns**ADC0820 – WD-RD Mode**t1 = tINTL= 800 ns**Acquiring an Analog Signal**• Input is a sinusoidal signal with peak to peak of 5 V • Voltage input in the range -2.5 to 2.5 V • Use Analog to Digital Converter ADC0820 • Input’s analog voltage 0 to 5 V • Requires adding 2.5 Volts to input signal before converted.**Op-Amp - Non-Inverting Adder**• Use LM741 Operational Amplifier • Eqs: Vo =V1 + v2 (for all resistors equal) Vo = (R1+R2)/R2 (V1 R4 + V2R3)/ (R3+R4)**References**• http://en.wikipedia.org/wiki/Analog_to_digital_converter • http://hyperphysics.phy-astr.gsu.edu/HBASE/Electronic/adc.html

More Related