Voltage Bandgap Reference PDF

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Laboratory Report Activity No. 2Bandgap Voltage ReferenceIn partial fulfilment for the course ECE132 - Mixed Signals-IC Design LaboratorySubmitted to Engr. Allenn D. Lowaton Faculty, Department of Electrical Engineering and TechnologyCOET, MSU – IITSubmitted by John Carlo Guinoo BS ECE – III TIntrod...

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Laboratory Report Activity No. 2

Bandgap Voltage Reference

In partial fulfilment for the course ECE132.1 - Mixed Signals-IC Design Laboratory

Submitted to Engr. Allenn D. Lowaton Faculty, Department of Electrical Engineering and Technology COET, MSU – IIT

Submitted by John Carlo Guinoo BS ECE – III T89

Introduction A bandgap voltage reference is a temperature independent voltage reference circuit widely used in integrated circuits. The goal of a voltage reference is to generate a stable voltage that is ideally independent of changes in temperature and other external factors such as power supply variations or circuit loading from a device. It commonly has an output voltage around 1.25 volts (close to the theoretical 1.22 eV). This circuit concept was first published by David Hilbiber in 1964. Bob Widlar, Paul Brokaw and others followed up with other commercially successful versions. Voltage references are electronic devices that can produce a constant amount of voltage. Ideally, its constant voltage output does not vary with respect to the loading, the changes in supply voltage, the changes in temperature, and varying manufacturing process. Commonly, voltage references are called voltage sources; but technically, voltage references are used to create voltage sources.

Objective •

To design a bandgap voltage reference using an ideal op amp.

•

To design a bandgap voltage reference using non-ideal op amp integrated with constant-gm current reference.

•

Take observe the changes of the output voltage with respect to the changes in temperature, voltage supply and different process corners.

•

Compare the two design of voltage reference.

HSpice Syntax for Ideal Op Amp

e vout1 vout2 vin+ vin- max=1.8v min=0 100,000 •

e - is an Hspice reserve word for ideal op-amp, just like M(for MOS), R(for resistor), C(for capacitor), etc.

•

out1 out2 vin+ vin- - are the nodes names for the outputs and inputs for a fully differential Op Amp (for a single-ended output Op Amp, vout2 can be connected to ground).

•

max – the maximum voltage, usually dictated by the supply voltage of the technology being used.

•

min = usually 0 v.

•

100,000 = the gain, the value can be specified according to preference.

Circuit Schematic

.OP Results

Simulation Results

Ideal Voltage Reference Avanwaves Result

Ideal Avanwaves (+) and (-) TC Result

HSpice Syntax for Non-Ideal Op Amp

Simulation Results

Non-Ideal Voltage Reference Avanwaves Result

Non-Ideal Avanwaves (+) and (-) TC Result

Calculations

Temperature Coefficient Formula:

𝑀𝑎𝑥 𝑉𝑟𝑒𝑓 −𝑀𝑖𝑛 𝑉𝑟𝑒𝑓 𝑇𝑒𝑚𝑝. 𝑆𝑤𝑒𝑒𝑝 ∗ 𝑉𝑟𝑒𝑓 @ 27 °𝐶

Ideal

TC =

Non-Ideal

850.3 V − 592.9 V 160 ∗ 734.5 V

TC =

TC = 2190.265 ppm / °C

850.4 V − 743.6 V 160 ∗ 594.7 V

TC = 2149.173 ppm / °C

Resistor Value Calculation Formula:

∂Vref ∂𝑇

= 𝛼1

∂Vb𝑒1 ∂𝑇

+ 𝛼2

∂Vb𝑒2 ∂𝑇

Ideal

∂Vref ∂𝑇

= 𝞪1

∂Vb𝑒1 ∂𝑇

Non-Ideal

+ 𝞪2

∂Vb𝑒2 ∂𝑇

R1

∂Vref ∂𝑇

= 𝞪1

∂Vb𝑒1 ∂𝑇

+ 𝞪2

∂Vb𝑒2 ∂𝑇

R1

0 = (-1.7822x10−3) + (R3)(1.7375x10−4 )

0 = (-1.7798x10−3 ) + (R3)(1.76219x10−4 )

R1 = R2 = (10.25) R3 = 71.805k Ω

R1 = R2 = (10.099) R3 = 70.6672k Ω

Using the new values for resistors R1 and R2 on the Ideal and Non-Ideal Circuit, we simulate the bandgap voltage reference on three different process corners namely TT, FF and SS.

Revised HSpice Syntax and Listing Result for Ideal Op Amp

Simulation Results Revised Ideal Voltage Reference Avanwaves Result (with respect to Temperature)

TT

FF

SS

Revised Ideal Voltage Reference Avanwaves Result (with respect to Voltage)

TT

FF

SS

Ideal Reference Voltage Values from the different Process Corners

Max Vref: 1.2398

TT

Min Vref: 1.1964 Vref @ 27°: 1.2398 Max Vref: 1.2153

FF

Min Vref: 1.2109 Vref @ 27°: 1.2148 Max Vref: 1.268

SS

Min Vref: 1.2635 Vref @ 27°: 1.2671

Calculations

Process Corners

Temperature Coefficient

Sensitivity

TT

21.875 ppm / °C

0.01194 %

FF

22.637 ppm / °C

0.01179 %

SS

22.690 ppm / °C

0.01176 %

Revised HSpice Syntax for Non-Ideal Op Amp

Revised HSpice Listing Results for Non-Ideal Op Amp

Simulation Results Revised Non-Ideal Voltage Reference Avanwaves Result

TT

FF

SS

Revised Non-Ideal Avanwaves (+) and (-) TC Result

TT

FF

SS

Non-Ideal Reference Voltage Values from the different Process Corners

Max Vref: 1.2327

TT

Min Vref: 1.2317 Vref @ 27°: 1.2317 Max Vref: 1.2085

FF

Min Vref: 1.2027 Vref @ 27°: 1.2065 Max Vref: 1.2670

SS

Min Vref: 1.2570 Vref @ 27°: 1.2608

Calculations

Process Corners

Temperature Coefficient

Sensitivity

TT

5.328 ppm / °C

0.04163 %

FF

29.931 ppm / °C

0.05388 %

SS

49.417 ppm / °C

0.00638 %

Discussion of Results

The initial bandgap voltage reference having R1 = R2 = R3 = 7k Ω has a temperature coefficient of 2190.265 ppm/◦C and 2149.173 ppm/◦C for the ideal and non-ideal, which is a relatively high value. With the intention of improving the performance of this voltage reference with respect to its dependence on temperature variation, R1 and R2 were both set to 71.805k and 70.6672k, for the ideal and non-ideal respectively; the formula and solving process included in the previous pages. A revised voltage reference was simulated in three different process corners TT, FF, and SS after modification of the resistors values. The results were improved as compared to the initial design; from 2190 ppm/◦C and 2149 ppm/◦C to less than 22 ppm/◦C for the ideal and values ranging from 5 to 49 ppm/◦C for the non-ideal. The output of the variation of the supply voltage reflects that the revised design has less than 0.1% sensitivity to the sudden changes in supply voltage in all three process corners. When we observe at the results with respect to the various process corners, there are noticeable differences among the processes especially in temperature variation. The supply voltage variation has roughly the same results in the three processes but observing closely to their values, there are differences although in the millivolts scale. Comparing the results of temperature variation with respect to process corners, it is clear that the TT process corner has better performance and has less susceptibility to changes in temperature compared to FF and SS process corners.

Conclusion

This laboratory activity enabled us to design a voltage bandgap reference and to integrate and simulate the previous designs, the two-stage operational amplifier and constant gm current reference along with the bandgap voltage reference into a single circuit design. By changing the values of the resistors R1, R2 and R3, the temperature coefficient of the voltage reference is greatly reduced and therefore improves the performance. The differences between the resultant values of the ideal op-amp and non-ideal op amp are due to actual MOS devices being used rather than the ideal device. Therefore, nonidealities are introduced. In addition, there is a significant difference on the performance of the bandgap voltage reference when using ideal and non-ideal components. It is expected that the design with ideal component performs better than with the design with non-ideal components. Nonetheless, the design with non-ideal components gives more realistic results and simulation.

References •

Arar, S. (2019). Introduction to Bandgap Voltage References. Accessed from https://www.allaboutcircuits.com/technical-articles/introduction-to-bandgapvoltage-references/

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Wikiwand: Bandgap Voltage Reference. Accessed from https://www.wikiwand.com/en/Bandgap_voltage_reference...