Chapter 12Data Converters: Basic ConceptsData Converters: Basic ConceptsEmbedded SystemA/D ConverterA/D Conversion – Pulse Code Modulation/Demodulation Analog-to-Digital A little Detour: Opamp Review OpampsClosed Loop Frequency ResponseComparatorsExampleBack to A/D Converters….A/D Conversion - TypesA/D ConversionA/D ConversionSuccessive Approximation A/D Converter CircuitSample and Hold CircuitCalculating Required Acquisition Time (TACQ)ExampleA/D ExamplesA/D ExamplesPIC18F4520 Analog-to-Digital (A/D) Converter Module (1 of 3)PIC18F4520 Analog-to-Digital (A/D) Converter Module (2 of 3)PIC18F2XK20/4XK20 Analog-to-Digital (A/D) Converter Module (2 of 3)PIC18F4520 Analog-to-Digital (A/D) Converter Module (3 of 3)A/D Control Register0 (ADCON0)A to D Control Register1 (ADCON1)A to D Control Register1 (ADCON1)A to D Control Register1 (ADCON1)Selecting the Analog PortA to D Control Register2 (ADCON2) (1 of 2)A to D Control Register2 (ADCON2) (2 of 2)A to D Control Register2 (ADCON2) (2 of 2)Reading the OUTPUT ResultsExample 12.3Board ConnectionExample: ExampleSlide Number 40Interfacing a Temperature Sensor (1 of 7)Interfacing a Temperature Sensor (2 of 7)Interfacing a Temperature Sensor (3 of 7)Interfacing a Temperature Sensor (4 of 7)Interfacing a Temperature Sensor (5 of 7)Remember ….Non-Inverting Voltage Level ShifterInterfacing a Temperature Sensor (6 of 7)Interfacing a Temperature Sensor (7 of 7)Digital to Analog (D/A, DAC, or D-to-A) ConversionAnalysis of a Ladder NetworkThe R/R2 Ladder NetworkExamining Digital-to-Analog Conversion Digital to Analog ConversionD/A Converter Circuits (1 of 4)D/A Converter Circuits (2 of 4)D/A Converter CircuitsD/A Converters as Integrated Circuits Example 12.4How can you generate a sine wave? Example – in C Read the link below for full library functions in <adc.h>Example in C – Monitor 3.3 V supply in a PC Power SupplySlide Number 63Slide Number 64LABReferences Backup slides….Generating a Ramp Waveform Using a D/A Converter (1 of 3)Generating a Ramp Waveform Using a D/A Converter (2 of 3)Generating a Ramp Waveform Using a D/A Converter (3 of 3)Slide Number 71Chapter 12Data ConvertersRead Section 19 of the Data Sheet for PIC18F46K20Data Converters: Basic Concepts Analog signals are continuous, with infinite values in a given range. Digital signals have discrete values such as on/off or 0/1. Limitations of analog signals Analog signals pick up noise as they are being amplified. Analog signals are difficult to store. Analog systems are more expensive in relation to digital systems.Data Converters: Basic Concepts Advantages of digital systems (signals) Noise can be reduced by converting analog signals in 0s and 1s. Binary signals of 0s/1s can be easily stored in memory. Technology for fabricating digital systems has become so advanced that they can be produced at low cost. The major limitation of a digital system is how accurately it represents the analog signals after conversion.Embedded System A typical system that converts signals from analog to digital and back to analog includes: A transducer that converts non-electrical signals into electrical signals An A/D converter that converts analog signals into digital signals A digital processor that processes digital data (signals) A D/A converter that converts digital signals into equivalent analog signals A transducer that converts electrical signals into real life non-electrical signals (sound, pressure, and video)So, how does A/D Converter works?A/D Converterhttp://www.cybercollege.com/tvp008.htm In order to change an analog signal to digital, the input analog signal is sampled at a high rate of speed. The amplitude at each of those sampled moments is converted into a number equivalent – this is called quantization.  These numbers are simply the combinations of the 0s and 1s used in computer language – this called encoding.A/D Conversion – Pulse Code Modulation/Demodulation PCM SignalModulationDemodulationAnalog-to-Digital  A simple hypothetical A/D converter circuit with one analog input signal and three digital output lines with eight possible binary combinations: 000 to 111 Shows the graph of digital output for FS V analog input The following points can be summarized in the above process: Maximum value this quantization process reaches is 7/8 V for a 1 V analog signal; includes 1/8 V an inherent error 1/8 V (an inherent error) is also equal to the value of the Least Significant Bit (LSB) = 001. Resolution of a converter is defined in terms of the number of discrete values it can produce; also expressed in the number of bits used for conversion or as 1/2n where n =number of bits The value of the most significant bit (MSB) -100- is equal to ½ the voltage of the full-scale value of 1 V. The value of the largest digital number 111 is equal to full-scale value minus the value of the LSB. The quantization error can be reduced or the resolution can be improved by increasing the number of bits used for the conversion7/8A little Detour: Opamp Review  http://www.engin.brown.edu/courses/en123/L ectures/DAconv.htm Some basics: http://www.seas.upenn.edu/~ese206/labs/adc2 06/adc206.html Check out the Applet on my webOpamps Ideal opamps Infinite BW Infinite voltage gain  Infinite input impedance  Zero output impedance Practical opamps Wide BW Very high voltage gain  Very high input impedance  Very low output impedancehttp://www.chem.uoa.gr/Applets/AppletOpAmps/Appl_OpAmps2.htmlClosed Loop Frequency Response Non-inverting Source is connected to the non- inverting input Feedback is connected to the inverting input If Rf and Ri are zero, then unity feedback used for buffering Av = 1+Rf/Ri Inverting Feedback and source are connected to the inverting input Av = - Rf/RiComparators Determines which input is larger  A small difference between inputs results maximum output voltage (high gain) Zero-level detection Non-zero-level detectionMax and minimumExampleVref = Vin(max).R2/(R1+R2)=1.63 VBack to A/D Converters….A/D Conversion - Types Can be classified in four groups: Integrator: Charges a capacitor for a given amount of time using the analog signal.  It discharges back to zero with a known voltage and the counter provides the value of the unknown signal. Provides slow conversion but low noise. 