Analog  Digital Conversion

Presentatie over: "Analog  Digital Conversion"— Transcript van de presentatie:

1 Analog  Digital Conversion
Properties: Resolution/ precision aantal bits Conversion time Max. sample frequency Prijs

2 Precision

3 Sample frequency

4 Aliasing

5 Analoog  Digitaal Conversie
Principes Successive Approximation Flash ADC Sigma Delta ADC

6 Successive Approximation

7 Flash ADC

8 Sigma-Delta ADC

9 SigmA Delta Converter type HI7190
Sample frequency: 10MHz, , 24 - Bit, High Precision, 22 - Bits Resolution

10 Resolution and Bandwith

11 Digitaal  Analoog (DAC)
DAC met R – 2R weerstanden Pulsbreedte modulatie (PWM)

12 Operational Amplifier

13 Optelschakeling OpAmp
1 V 2 k Bereken Vo

14 LSB = onderste of bovenste weerstand?
DAC Ropamp = 1 k V0 = ? LSB = onderste of bovenste weerstand? 1 4 V

15 DAC met R-2R netwerk

16 Pulse Width Modulation
Digital Analog Converter Toepassing: servomotorregeling Modulation frequency Duty Cycle = verhouding hoog/laag

17 Pulse Width Modulation
Digital Analog Converter Toepassing: servomotorregeling Volt Volt Volt Modulation frequency > 600 Hz (hangt van de traagheid van de motoras) Duty Cycle = verhouding hoog/laag

18 Sensors & Data Acquisition Systems
Amplifiers & Analog Filters Sample & Hold ADC

19 Transducers Sensors Small Signals Signal Conditioning Wiring/Grounding
Phenomena  ADC Transducers Sensors Small Signals Signal Conditioning Wiring/Grounding

20 Voorbeeld van een sensor: rekstrookje
R = weerstand = soortelijke weerstand L = lengte A = doorsende

21 Strain Gauge / Rekstrookje
Dummy Gauge:Temperature compensation

22 Strain Gauge

23 Applications Force sensors Spirometers Truck weigh stations
Position sensors

24 Force to Voltage: Weatstone Bridge Circuit
R1= R2= RG1= RG2 = 1000 ; RG MAX= 10 ; VEX = 5 V

25 Intermezzo on Cascaded Resistors
Vin Vout R1 R2

26 Intermezzo on Cascaded Resistors
Vin Vout R1 R2

27 Force to Voltage: Weatstone Bridge Circuit
In rust: R1= R2= RG1= RG2 = 1000 ; RG MAX= 10 ; VEX = 5 V

28 Assignment: Calculate the differential input voltage for the ADC
In rust: R1= R2= RG1= RG2 = 1000 ; RG MAX= 10 ; VEX =Vin= 5 V

29 Sensor, Amplifier & ADC Amplifier Weatstone bridge + A ADC - mV/bit?

30 Assignment: Specify the gain of the amplifier
Input range of the ADC = 5 V The ADC = 12 bit

31 Opamp

32 The ideal Amplifier 2. Input impedance--infinite
1. Gain--infinite 2. Input impedance--infinite 3. Output impedance--zero 4. Bandwidth--infinite

33 Closed Loop Inverted Amplifier

34 Assignment: Design the amplifier
Voor Weatstone bridge: welke versterker? R1 = ? R2 = ?

35 Beter algemeen systeem Sensor-output- & ADC-input impedance
Rsensor Vsensor VADC RADC

36 Measurement errors - t.g.v. mismatch sensor-output-/ADCinput- impedance t.g.v. aardlussen t.g.v. te lage “CMRR”

37 Sensor output impedance
Strain Gauge Vs = 50 mV; Rs = 1000  Thermocouple Rs < 20  pH Electrode Rs = 100 M

38 Rsensor RADC Error (%) 10 k 1 M 1 1 k 100 k 2 100  3 50 k 4
Assignment: Determine the measurement error as a result of the mismatch sensor-resistance and the ADC input-resistance Rsensor RADC Error (%) 10 k 1 M 1 1 k 100 k 2 100  3 50 k Sevo motor potmeter ADC PIC’s 16F876 4

39 Measurement error t.g.v. mismatch sensor-output-/ADC input- impedance
Stel: 10 bits ADC; Bij welke van de 4 systemen is de fout > 1 bit? Zijn de berekende errors absoluut of relatief? Hoe kunnen deze fouten opgelost worden? Hardwarematig ….? Softwarematig …..?

40 Measurement errors - t.g.v. mismatch sensor-output-/ADCinput- impedance t.g.v. aardlussen t.g.v. te lage “CMRR”

41 Ground-Referenced / Floating Signal Source

42 Grounded Measurement System

43 Floating / Differential Input Measurement System

44 Grounded Signal source/ Grounded Measurement System  aardlus

45 Grounded Signal Source/ Floating Measurement System

46 Floating Source/ Floating Measurement System
R1 = R2 (10k < R < 100k)

47 Instrumentation Amp.

48 Common mode & Differential mode narekenen
Plaatje aanpassewn 2.525 V 2.475 V 5.0 V Common mode = 2.5 V Differential mode = 25 mV

49 Common Mode Rejection Ratio (CMRR)Beter 20 log
ingangsbereik ADC = 0 – 5 Volt; Versterkingsfactor 200; 12 bits ADC Eis: fout mag max. 1 bit zijn. 12 bits ADC  1 : 4096; 1 LSB = 5000 mV/4096 =  1,25 mV. Bij ingang versterker is dit 1,25/200 = 6,25 V CMRR (dB) = 20 log (Differential mode/ Common Mode) = 20 log ( 6,25 V / 10V)  100 dB. (factor 10000) 20 dB = factor 10

50 Toepassing Unshielded Twisted Pair EMS