Op-amp Block

The op-amp blocks are breadboard-friendly but can also be plugged into one another for developing complex circuits with minimal additional components through a simple 5 pin interface. For input, the interface consists of IN-, IN+, GND, V-, and V+. On the output side you can select via solder jumpers where the block’s output goes to the following block – either to IN- or to IN+. Plus it passes through the power pins, such that all blocks share the same power supply.

An additional input interface is present on the bottom of the block, with the IN- and IN+ disconnected by default, so power can be injected into an analog chain leaving the inputs available for sensors. The bottom IN pins can be enabled by solder jumpers, for example to provide a fixed bias voltage somewhere in the analog chain.

Power module

A Type-C power module can supply voltages to the analog chain from any USB port. It provides a choice for V+ of either 3.3V or 5V, and for V- either GND or -0.23V (when you need the output reach true 0V). The OPA357 is specified for supply voltages between 2.7V and 5.5V so any combination of V+ and V- will keep it happy. Two potentiometers on the power module can provide fixed biases for IN- and/or IN+.

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For the radiation detector I’m working on I had to do my first analog design. I knew it wouldn’t be very straight-forward and I’d be going back and forth between simulations in PSpice for TI and trying out circuit prototypes. The detector analog front-end needs to be fairly fast and most interesting op-amps come in tiny packages. I’d also want to avoid long traces and high parasitic capacitances in the feedback loop for this type of prototyping.

My solution was to make some versatile plug-in modules with a few different op-amps that I can just swap out during testing. Specs:

• 3 different op-amps supported (on different PCBs): OPA357, AD8038, and TLR341. Op-amp pinouts being what they are you can actually fit a lot more
• Decoupling capacitors on the module
• Same pin-out for all 3 boards to easily swap them out
• Flexibility to implement different feedback networks on the module using 0603 components and solder bridges
• Op-amp enable pin accessible, but can also be solder bridged to Vcc

Then I could also have the same circuit but in several versions (e.g. with different gains) that I could swap out. This allowed me to independently figure out the block diagram and each amplifier's feedback network.

Schematic

The design allows connecting inputs and output directly (through solder bridges) to the op-amp, or through 0603 components. Only negative feedback is implemented in the schematic, but if you're willing to have some flying leads you can do pretty much anything :)

PCB versions

I made 3 versions for different types of op-amps. By far the one I used most is the OPA357 as it's a very fast and flexible general-purpose chip.

Use case

I used these modules to develop the analog section of the radiation detector I'm working on. They allowed me to decouple the "block diagram" mess located on a perfboard, from each block's paramers (e.g. gain, shaping time).

On the left there's a very early prototype while I was trying to figure out the block diagram. On the right is a late stage prototype once the block diagram was sorted out, such that I could swap modules out for optimization.