# BEng Step Graph.. 11 Figure 10: 12

BEng (Hons) Electrical Electronic Engineering TM625: Electronics and Control Assignment 1 S13302 Contents Table of Figures. 3 Abbreviations. 4 Task 1.

5 1. Weighted resistor DAC.. 5 2.

R-2R DAC.. 6 3. Successive Approximation ADC.. 7 Task 2.

8 1. Explain circuit operation and modes. 8 2.

Acquisition time. 9 3. Aperture time. 10 4. Drift Rate.

10 5. Settling time. 11 6.

Hold step. 11 7. Turn – off time. 12 8. Calculate the time required for the capacitor voltage to reach a value within 1 percent of the input voltage.

13 Task 3. 14 1. TF = (2S+9)/(S2+2S+4), Gain of 2. 14 2. PID.. 15 3. PI 17 4.

PD.. 19 5.

Comparison of the performance of PI, PD and PID systems. 20 Task 4. 20 References. 21 Table of Figures Figure 1: Weighted Resistor DAC Circuit 5 Figure 2: R-2R Ladder DAC Circuit 6 Figure 3: Successive Approximation ADC.. 7 Figure 4: Sample and hold circuit 8 Figure 5: Acquisition time graph..

9 Figure 6: Aperture Time Graph.. 10 Figure 7: Drift Rate Graph.. 10 Figure 8: Settling Time Graph.. 11 Figure 9: Hold Step Graph..

11 Figure 10: 12 Figure 11: RC Time Constant Table. 13 Figure 12: Transfer Function System..

14 Figure 13: PID System Response. 14 Figure 14: PID Steady State Error 14 Figure 15: PID Values. 14 Figure 16: PID System.. 15 Figure 17: PID Response.

15 Figure 18: PID Gain.. 15 Figure 19: PID Steady State Error 15 Figure 20: PID Derivative. 15 Figure 21: PID Intergrator 16 Figure 22: PI System.. 16 Figure 23: PI System Response. 16 Figure 24: PI Steady State Error 16 Figure 25: PI Integrator 17 Figure 26: PI Gain.

. 17 Figure 27: PI Derivative. 17 Figure 28: PD System.. 18 Figure 29: PD System Response.

18 Figure 30: PD Steady State Error 18 Figure 31: PD Integrator 18 Figure 32: PD Gain.. 18 Figure 33: PD Derivative.

18 Figure 34: Flash ADC Circuit Build. 19 Figure 35: Flash ADC Circuit Build. 19 Figure 36: Flash LEDs.

19 Abbreviations DAC Digital to Analogue Converter ADC Analogue to Digital Converter MSB Most significant bit LSB Least significant bit SAR Successive Approximation Register FET Field-effect transistor PID Proportional–Integral–Derivative Controller Task 1 1. Weighted resistor DAC Figure 1: Weighted Resistor DAC Circuit The weighted resistors DAC circuit consists of resistors and an operational amplifier. Vout is the inverted sum of all the input voltages.

If the values of the input resistors are set to multiples of two e.g. 1.25kohm, 2.5kohm, 5kohm, 10kohm, the output voltage would be equal to the sum of the input voltages multiplied by the ratio of input resistors and feedback resistor, V1*(10k/1.25k), V2*(10k/2.

5k), V3*(10k/5k) and V4*(10k/10k). Therefore, V1 corresponds to the most significant bit (MSB) while V3 corresponds to the least significant bit (LSB). 2.

R-2R DAC The circuit for a 4-bit DAC using binary weighted resistor network is shown below: Figure 2: R-2R Ladder DAC Circuit An alternative to the Weighted Resistor DAC is the R-2R Ladder DAC. This type of DAC uses two values, R and 2 * R. when each input is supplied with a logic level 0 or a logic level 1 the output will be the voltage equivalent and the binary input.

Its advantage of the weighted resistor DAC is that it has fewer different values. The output can be given from the equation: Where: · Rf = R9 (20,000Ohms) · Ra = R7 (10,000Ohms) · N = number in decimal form i.e. 1001 = 9. · n = number of bits in the system i.

e. 4 bits in total. · Vr = reference voltage, i.e. 5V Therefore, to calculate the output if the binary input is 1001 would be; 3. Successive Approximation ADC Figure 3: Successive Approximation ADC The Successive Approximation ADC is a convertor that continuously converts an analogue signal into a digital output by a binary search method. The SAR ADC start by trying all the values of bits starting the MSB and finishing with the LSB.

For example, a SAR ADC with 4-bit resolution. Vref = 1V Vin = 0.6V. Vadc = internal comparator voltage The ADC starts with the MSB (Bit-3). Vref is divided by 2 and compared with Vin.

As Vin is greater than Vref/2, it turns MSB to a logic 1. 1 X X X The next calculation is for the MSB-1 (bit-2), Vin is compared to Vadc = Vref/2+Vref/4 = 0.5+0.25V = 0.75.

As Vin < Vadc (0.75V) bit 2 is turned off. 1 0 X X For MSB-2 (bit-1) is compared with Vref/2 + Vref/8 = 0.

625. as 0.6V < 0.625, the MSB is turned off.

1 0 0 X For MSB-3 (bit-0) is compared with Vref/2 + Vref/16 = 0.5625. as 0.6V > 0.5625, the MSB is turned on. 1 0 0 1 Task 2 Figure 4: Sample and hold circuit 1.

Explain circuit operation and modes The sample and hold circuit is used to capture an analogue voltage. There are two modes – sample (also known as track) and hold, below is a description of the operation of each. In the sample mode, the sample control node is held to a logic 1 – the buffered input voltage flows the FET and charges the capacitor. In this made the output voltage will match the input voltage. In the hold mode, when the sample control node is a logic 0, the FET is turned off. At this point the capacitor is disconnected from the input circuitry and retains the sampled voltage, this is then slowly discharged through the resistor and the op-amp to create a Vout.

2. Acquisition time Figure 5: Acquisition time graph The acquisition time is the length of time that the circuit must remain in the sample mode to acquire a full-scale output. The maximum acquisition time arises when the hold capacitor charges to a full-scale voltage change. This period depends on the size of the hold capacitor.

The acquisition time can be reduced by choosing a smaller value capacitor, however this will also increase discharge rate. 3. Aperture time Figure 6: Aperture Time Graph The aperture time, is the delay between the hold signal being applied and the input signal being disconnected from the hold capacitor. 4.

Drift Rate Figure 7: Drift Rate Graph This affect is known as droop rate expressed in V/us, during the hold mode there are errors in the hold capacitor, amplifiers and switch. If a leakage current flows in or out of the hold capacitor, this would slowly reduce or increase the voltage in the capacitor. 5. Settling time Figure 8: Settling Time Graph The settling time is the time taken for the output voltage to stabilise within a specified error band after a hold command has been given. 6. Hold step Figure 9: Hold Step Graph The hold step is the voltage at the output due to the sample-to-hold transition. It is caused by a transfer of charge to the hold capacitor due to the opening of the switch. 7.

Turn – off time Figure 10: 8. Calculate the time required for the capacitor voltage to reach a value within 1 percent of the input voltage. · ON resistance = 30? · C1 = 1µF Time Constant RC Value Voltage percentage of max.

0.5 time constant 0.5T = 0.5RC 39.

3% 0.7 time constant 0.7T = 0.7RC 50.3% 1.

0 time constant 1T = 1RC 63.2% 2.0-time constants 2T = 2RC 86.5% 3.0-time constants 3T = 3RC 95.0% 4.0-time constants 4T = 4RC 98.2% 5.

0-time constants 5T = 5RC 99.3% Figure 11: RC Time Constant Table The formula to calculate the time the voltage in the capacitor charges to within 1 percent of the input voltage is: Therefore, Task 3 1. TF = (2S+9)/(S2+2S+4), Gain of 2 Figure 12: Transfer Function System Figure 13: PID System Response The graph above shows the system response, settling at around 7 seconds.

Figure 14: PID Steady State Error The graph above shows a steady state error of 0.0001 Figure 15: PID Values P = 0.2222222222, I = 0.00000000001 D = 0.00000000001 2.

PID System Figure 16: PID System Figure 17: PID Response The above graph is the response of the PID system, shown to settle at around 8 seconds. Figure 18: PID Gain G = 0.1 Figure 19: PID Steady State Error The above graph is the steady state error of the PID system, with an error of 0.0001. Figure 20: PID Derivative D = 50 Figure 21: PID Intergrator I = 0.

1749 3. PI System Figure 22: PI System Figure 23: PI System Response The graph above is the response of the PI system, shown to settle at around 8 seconds. Figure 24: PI Steady State Error The graph above is the steady state error of the PID system, with an error of 0.0 Figure 25: PI Integrator I = 0.1749 Figure 26: PI Gain G = 0.1 Figure 27: PI Derivative D = 0 4.

PD System Figure 28: PD System Figure 29: PD System Response The graph above is the response of the PD system, shown to settle at around 9 seconds. Figure 30: PD Steady State Error The graph above is the steady state error of the PID system, with an error of 0.0008 Figure 31: PD Integrator Figure 32: PD Gain Figure 33: PD Derivative 5.

Comparison of the performance of PI, PD and PID systems The PI, PD and PID systems Task 4 Figure 34: Flash ADC Circuit Build Figure 35: Flash ADC Circuit Build Figure 36: Flash LEDs ReferencesFigure 5-9 – http://www.analog.com/media/en/training-seminars/tutorials/MT-090.pdf