Wien Bridge Oscillator And Op-Amp Differential Amplifiers: Theory And Design

1. Application of voltage amplifiers into areas such as instrumentation.

2. VHDL design of a finite state machine.

Assessment criteria

The work will be assessed against an approved marking scheme. A perfectly correct technical solution presented to high professional standards with commentary and insights including detailed references can expect to be awarded >80%. Marks will be lost for errors, missing sections, poor presentation and lack of detail in analysis and commentary.

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1. Discuss factors that influence the set up of an oscillator type such as a Wien bridge i.e. criterion for oscillation, control of amplitude and so on. Additionally you are required to simulate a Wien bridge of frequency kHz first two digits of your SID.

2. i) Discuss and analyse the single operational amplifier in a differential amplifier mode shown in figure 1 to determine its input to output voltage characteristic.
ii) How does the characteristic simplify if it assumed that R2 = R4 and R1 = R3.
iii) Why is this configuration not really suitable for application as an instrumentation amplifier?

Part-2

1. Produce a VHDL design unit (entity & architecture pair) to model the state machine as shown in the state diagram below (Figure 2). If your SID is an even number then X can be replaced by 1, otherwise it should be replaced with 0:

Insert your VHDL model design and simulate it.

2. There are different hardware target solutions which can be used to implement a digital system. Write a short literature review discussing each of them mentioning their advantages and disadvantages.

Note: it is very important that the work submitted is an individual effort. The penalties for plagiarism are severe.

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Construction and Design of Wien Bridge Oscillators

Wien bridge oscillator is one type of oscillator. The oscillator has a high resonant frequency, low distortion. The oscillator has no input (Lerner, 2016) .The Wien bridge oscillator was developed by Wien (ElProCus - Electronic Projects for Engineering Students, 2018). It is used to measure the impedance value. It has four resistors and two capacitors.

When  R1 =R2=R,AND C1=C¬2=C              

The stable condition was given below

 Given frequency is f =57 KHZ

By substituting the frequency value to the above equation

R=1K?

C=2.79nF

An operational amplifier is a voltage amplifier.it produces output that is equal to the difference of its inputs(COMPARATIVE ANALYSIS OF TWO STAGE OPERATIONAL AMPLIFER, 2015). Operational amplifiers often called as opamp . The opamp is one type of differential amplifier. Opamp has two inputs namely inverting and non-inverting terminals.

The differential amplifier is electronic amplifier.it is used to amplify the difference between the input voltages and reduces the common voltages.it has two modes of operations as common mode and differential mode. For good differential amplifier differential mode gain should be high (Guo, 2017).

CMRR of a differential amplifier is very important characteristic of a differential amplifier that is given by,

                                                    CMRR=Ad/Ac

                                  CMRR value of differential amplifier should be high.

       The ideal opamp is given by

                         V_out = A (V_in⁺ - V_in^-)

  Where, A is gain of  the amplifier

     V_in⁺ is non inverting terminal input voltage

     V_in^- is inverting terminal input voltage

     From given figure

    When making V2 short-circuited Non inverting output is given by,

                          V_out⁺ = V1(R2/(R1+R2)).(1+(R4/R3)

    Similarly, when V1 is short-circuited inverting output is given by

                          V_out^- = -V2(R4/R3)

   The total output of a Differential amplifier is

                          V_out = -V2(R4/R3) + V1R2/(R1+R2).(1+(R4/R3)

   When R2 = R4 and R1 = R3.the output will be reduced to

                          V_out = R2/R1(V2-V1)

• Instrumentation amplifier requires large gain. A single differential amplifier does not give that amount of gain.
• Output voltage gets affected if we use a single differential amplifier for instrumentation amplifier. Because of resistor mismatching(Watson and Castro, 2012).
• Instrumentation amplifier need three stages of opamps to reduce the common mode gain
• In differential amplifiers, common mode values are present which makes very difficult to amplify the small signals.  

Because of these reasons Instrumentation amplifier requires the op amps. Two additional opamps are used to reduce low resistance. The output of these opamps is given to the second stage differential amplifier.

Here the VHDL code for the given problem was developed and given below.  The given state machine starts with SA as starting state and ends with the SC state(COHEN, 2013). Between the starting state as well as ending state the state SB was situated. So here totally there are three nodes. Each node capable of processing the input as well as output (Ece-research.unm.edu, 2018). The direction of the transformation depends upon the input statement given by the user. In this problem, if the state SB has the odd number the x value becomes 0, If the SB value may be even the value of x will become one. For the above constraints, the below code was developed. We can able to simulate this code by using the “Xilink SE”. Here the code was attached (Ashenden, 2011).

Theory and Function of Operational Amplifiers in Differential Amplifiers

“Jonathan Turner” carried out the research on the VHDL design and simulation.  From his research, he found the various advantages as well as disadvantages of the various VHDL tools. The advantages of VHDL tools are, speed up the computation process, improve the flexibility of the design, to minimize the cost of the simulation, and reduce the wastages of the testing. These are the positive elements of the VHDL design and simulation according to the author. And he also noticed some of the drawbacks of the VHDL simulation process. And they are Lower accuracy, because the lower no of constraints, cost of the simulation tool, and the computation process were highly complicated. These are the results of his research. These are considered for this research work.

“Valentina Stoyanova Kukenska” carried out the research on the VHDL design of structural model and behavior model. From his research, he found the various advantages and disadvantages in the structural and behavior model. The structural model has two stages, top-down designing and uptown designing. By the top down simulation, we can able to check the error, so it has the higher processing speed.  The up-down process consumes the higher time for calculation than the Top down method. But it gives the more details about the process.  And also he noticed some drawbacks in structural model and behavior model. The structural model was limited to sequential circuits only. It is a step by step process the time delay will be occurring in this model. These are the results of his research .these are considered for his research work.

“Muzakkir Mas’ud Adamu” carried out the research of VHDL design and simulation. From his research, he founded the various advantage as well as disadvantages of the various VHDL tools. Here these are considered for this resource. The advantages of VHDL design techniques are to design the digital design flow for the low power embedded products. In a computer application, the usage of flexibility can change the reducing the cost of system software. The circuits are design and manufacturing for the integrated forms. The device speed was high and its range was GHz to THz.The transmission of data to be encrypted. The disadvantages are the IC cannot be easily portable. The cost of the tool will be high. The real-time signal processing will be no guarantee. The approximation errors will occur. It is expensive and complex.

Advantages and Disadvantages of VHDL Design and Simulation of Digital Systems

Based on the study carried out by Aziza I. Hussein et al. summarized the following advantages and disadvantages. The highly complex design is easily designed as well as simulated by using those kinds of simulation software. Also, it provides the good and reliable results for the system. Highly complex codes are easily simulated by this software. According to this author, these points are the advantages of the VHDL design and simulation software. But this software has some disadvantages also. For the single-use, this software was too costly. Also, it has some limitations in the digital design developing stage.

Rajesh Kumar Gupta carried the research and he found the following advantages and disadvantages. Here we can able to improve the overall effectiveness of the embedded system design process. Because this method reduces the time required to design as well as check the system. And also the overall amount spent on the prototyping and testing was reduced. All the simulations were done by the computer so the accuracy was higher than the manual calculation and testing process. We can able to optimize the shape, size power requirements. By this simulation we can able reduce the complexity involves in the gate array designing. The above-described points are considered as the advantages of using the VHDL design and simulation for developing the digital systems. But it has some disadvantages also, for example, the operating procedure for those kinds of software tools are highly complex in nature. So it needs highly trained employees to do those jobs. The initial price of those software tools is also high. That also requires high-level system configurations.

References

Ashenden, P. (2011). The designer's guide to VHDL. Amsterdam: Morgan Kaufmann Publishers.

COHEN, B. (2013). VHDL CODING STYLES AND METHODOLOGIES. [S.l.]: SPRINGER-VERLAG NEW YORK.

COMPARATIVE ANALYSIS OF TWO STAGE OPERATIONAL AMPLIFER. (2015). International Journal of Advance Engineering and Research Development, 2(04).

Ece-research.unm.edu. (2018). VHDL Introduction. [online] Available at: https://ece-research.unm.edu/jimp/vlsi/slides/vhdl.html [Accessed 30 Jun. 2018].

ElProCus - Electronic Projects for Engineering Students. (2018). Wien Bridge Oscillator Circuit Theory and Working - Elprocus. [online] Available at: https://www.elprocus.com/wien-bridge-oscillator-circuit-working/ [Accessed 30 Jun. 2018].

Guo, J. (2017). A low-voltage sense amplifier with two-stage operational amplifier clamping for flash memory. Journal of Semiconductors, 38(4), p.045001.

Lerner, L. (2016). The dynamics of a stabilised Wien bridge oscillator. European Journal of Physics, 37(6), p.065807.

Watson, J. and Castro, G. (2012). An Ultra-Low Noise Instrumentation Amplifer Designed for High Temperature Applications. Additional Conferences (Device Packaging, HiTEC, HiTEN, & CICMT), 2012(HITEC), pp.000082-000086.