Due Wednesday 2018-04-18 at the start of class.

1. Op amp parameters

1.1. Goal

There some aspects of a circuit’s overall performance that are not sensitive to an individual component’s specifications and other aspects which are directly set by the performance of a single part. After designing the circuit topology and schematic, it is the engineer’s job to select which specific models of devices to use for each schematic element.

For opamp circuits, the variation of a gain or frequency response is mostly a function of the precision of the passive components (R, C, etc.). Indeed, this is a great advantage to opamp-based circuit design since precision semiconductors are usually much more expensive than precision passives. In these cases, it is required to select an opamp model that is good enough. It is a waste of money or rarely necessary to use a device with too good of performance!

There are hundreds of opamp models to choose from. The table lists several common, popular, and in-stock opamps. They were chosen also since they represent a range of technologies and performance balances, optimized for different applications.

Pay attention to the trade-offs between the various parameters. You may also find it interesting to also find the price of each model (use quantities of 1000 for the price).

1.2. Tasks

Begin with the handout from Monday’s class: 2018-04-16_opamp-table.pdf
Use the datasheets found at 341 Google Drive folder docs.

  • Start a spreadsheet of your own.

  • Find the parameters in the columns for each amplifier.

  • Add 2 columns to your spreadsheet.

    • Metric GBW / Isupply in units of MHz / mA.

    • Transistor type of the input differential stage.

  • Plot the requested two scatter plots.

Hand in one page with the (well-labeled) plots and the tables. Write a 2+ sentences about your observations of the trends you see in the various data points (over time, corellations between parameters, etc.).

2. Opamp model simulation

2.1. Goal

This exercise is to match the low-frequency gain Av0, -3 dB frequency fH, and unity-gain frequency fT between the various views of our discrete opamp:

opamp model
Figure 1. Small-signal opamp model

2.2. Tasks

Begin with the circuit of Small-signal opamp model.

Build this circuit in LTspice or CircuitLab [1]

  • Set Gm1 to be value of gm of the input differential pair transistors Q1 and Q2 of schematic Discrete opamp schematic.

  • Set R1 to be the value of the equivalent total small-signal resistance between node 2 and GND in the full schematic Discrete opamp schematic.

  • Set R2 to be the value of the small-signal resistance between node 4 and GND.

Simulate the frequency response (.ac analysis) of this amplifier. Measure the following parameters:

  • Low-frequency gain Av0 = vout/vid

  • -3 dB frequency fH

  • Unity-gain frequency fT

Hand in:

  • Plot of the magnitude and phase response over an appropriate frequency range.

  • Annotate this plot with the three measurements.


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Figure 2. Discrete opamp schematic

1. Remember that you have access to the full, paid, version with your Valpo email.