ELEC0151: Simulation Design Coursework Brief 2025

Simulation Design 1:

A fully differential biopotential amplifier design has been shown in [1] which is based on an earlier work [2]. A fully differential amplifier distinguishes itself from a single ended design, similar to the one shown in [3].

Assuming a single regulated power supply is available, your task is to evaluate and re-design the proposed design in [1] for a wearable solution through simulation and produce a document no longer than 3 pages that summarises your findings/design.

In your evaluation, you should use different op-amps compared to those used in [1] justifying your choices. Your op-amp selection, beyond evaluating the information available in datasheets, can involve simulation studies. As part of the submission, you should propose two different op-amps for this design, demonstrating their viability. For every passive component also, you should clearly justify the values you have selected either through analysis, discussion or simulation.

You should also redesign the circuit for a range of differential gain values (e.g., 200 to 2000 if viable), and at least for three gain values, to identify key limiting factors for this differential gain. One of the points you should consider is that input signals may have different DC offsets. You should evaluate what the permissible level of the differential DC offset is if that is found to be a limiting factor. The frequency of the target differential signal does not exceed 2 kHz.

Bonus tasks: You should investigate if selecting resistors from different ranges have an impact where only the ratios are theoretically important. You should also investigate the impact of variations in the values of passive components in general. These variations can include both tolerance variations (e.g., 1% or10% resistor tolerances) or sweeping values in a wider range where relevant to evaluate the variation in, for example, time constants or break frequencies.

Throughout, you should decide what set of simulation setup and results can best evaluate a given aspect of the circuit under investigation. Part of your results can include replicating the results in [1] where relevant. For example, CMRR analysis is among the most important investigations you should conduct for this application.

References

[1] Spinelli, Enrique M., et al. "A fully-differential biopotential amplifier with a reduced number of parts." IEEE Transactions on Instrumentation and Measurement 71 (2022): 1-8.

[2] Spinelli, Enrique Mario, et al. "A novel fully differential biopotential amplifier with DC suppression." IEEE transactions on biomedical engineering 51.8 (2004): 1444-1448.

[3] Spinelli, Enrique Mario, Ramon Pallàs-Areny, and Miguel Angel Mayosky. "AC-coupled front- end for biopotential measurements." IEEE transactions on biomedical engineering 50.3 (2003): 391-395.

Simulation Design 2:

Howland current pump (HCP) can be used when precise bidirectional or AC current should be passed through a load. The “basic” HCP as referred to in [1] is the originally proposed design. Due to a number of shortcomings of the basic design, the “improved” HCP is now the standard approach for most applications [1], [2]. Various other improvements have been suggested to the standard approach in the literature [2], [3], [4].

Assuming you have access to regulated power supplies of your choosing and signal generators with controllable attributes, you should first evaluate the  basic HCP and demonstrate  its shortcomings where possible using appropriate simulation setups. You can carry out this investigation using an op-amp of your choosing, justifying your choice. You should then design a current source based on the improved HCP. You should create a design capable of supplying currents from 0.5 mA to several tens of mA to loads ranging from 500 Ω to several kΩ over a range of frequencies up to about several MHz. You can apply any necessary adjustments needed to the improved HCP, as suggested in the literature, to accommodate the design specifications and to consider any other practical considerations including the cost and stability. You should present sufficient evidence to justify your choice of the op-amp(s). You should, overall, propose two suitable op-amps and demonstrate their viability in each case.

Bonus tasks: Investigate the impact of resistor tolerances in your design. Also investigate the performance of your design where the resistive load also has a capacitive load in parallel with it.

You should summarise your investigations and design in a document no longer than 3 pages. Include all evaluations and the necessary results that demonstrate you have fully or partially met the design specifications. One important  metric is the current accuracy which should  be included. If you do not fully meet the design criteria, you should appropriately discuss the outcome.

References

[1] Texas Instruments "An-1515 a comprehensive study of the Howland current pump." Application reportSNOA474A (2008 – Revised 2013).

[2] Lam, Ignacio Vazquez. "Analysis of improved Howland current pump configurations." Texas Instrument (2023).

[3] Mahnam, Amin, Hassan Yazdanian, and Mohsen Mosayebi Samani. "Comprehensive study of Howland circuit with non-ideal components to design high performance current

pumps." Measurement 82 (2016): 94-104.

[4] Tucker, Aaron S., Robert M. Fox, and Rosalind J. Sadleir. "Biocompatible, high precision,

wideband, improved Howland current source with lead-lag compensation." IEEE Transactions on Biomedical Circuits and Systems 7.1 (2012): 63-70.

Simulation software:

You can use the simulation software package of your choosing. Some examples include:

LTSPICE,TINA-TI, or Multisim.

Submission and marking guidelines:

Please submit one .pdf file including entries for both Simulation Design tasks (maximum of 3  pages for each entry). The list of references for both entries should be included in one page at the end which does not count towards the page limit. You can also have a cover page for your submission if needed which will not count towards this page limit either.

Marking guidelines:

Organisation, methods and simulation setup (8/20)

For each entry, your submission should start by a paragraph summarising your understanding of the circuit under investigation in which you should also highlight the key findings of your study.

You should clearly but briefly describe your design approach. For example, if relevant, you should explain the specific designs/adjustments you have made from different options available, how you have selected components considering the range of available options and demonstrate any calculations/analysis you have done. You should also show the simulation setup, and indicate briefly how you have used the setup to perform the different studies you have conducted. Where multiple steps are involved, organise these steps in sections to improve readability.

Results and discussions (8/20)

It is very important that you present your results in a way that they are easily understandable and you should think carefully what the best set of results are to present. Mark is allocated to both presentation of results as well as the outcome (i.e., whether you have met the design and evaluation brief). You should clearly but briefly describe your results and more importantly discuss them, highlighting implications and causes of specific observations. Very importantly, where you cannot meet the design specifications, discuss clearly why you think that is the case.

Appropriate use of external sources and referencing (4/20)

Please use IEEE referencing style when you use external sources. Only use authoritative sources and ensure your design decisions are sufficiently supported by the existing literature. Always compare your finding with what you find in the associated literature. By appropriate use of references, you can avoid repeating description of methods and refer the reader to appropriate resources. This way, you can use the space available to you more efficiently.

The 3-page limit per entry is not a target. For example, if you can convey all the necessary information in two pages, you should do that.