Signal Generator

ELAB-Signal-Generator

A square wave generator with adjustable frequency, gain, and offset control. Designed as a part of UBC's ELAB PCB design course.

Skills used in this project

KiCad, Analog Circuit Design, Hand Soldering, Testing/Validation

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Design

The design for this signal generator is not complex, this is because it's main purpose was to provide an opportunity to design and assemble a PCB from the start to finish of the production cycle. This included schematic capture, component/footprint library creation, component layout, laying traces, and laying polygon pours. In the second stage of the course, we received our boards and components and assembled them using hand soldering, and tested them using an oscilloscope to view our signals and test the various adjustments.

Power Supply

The signal generator utilizes +/-5V rails to be able produce a maximum of a 10V peak-to-peak signal. 15V comes from a barrel jack connections from a wall adapter, which is then regulated using the LM7805 to drop to it to +5V. This rail then feeds into the MAX889 that produces the complimentary -5V rail. Output capacitors are used to help with input noise, and output voltage ripple.

Signal Amplifier

The square wave signal is generated by the NE555, that includes a frequency adjust potentiometer. This signal is then fed to the AD8039 with two amplifier stages to control gain and offset respectively. Additional bypass capacitors are placed on the op-amps power rails to help with further noise reduction and to help stabilize voltage. Finally, a 3.3V peak-limiter zener diode is placed on the output which can be engaged with the use of a jumper.

PCB Design

With this being my first attempt at PCB design, there is room for improvement with my traces decisions component placement. With this project, we were constrained on the size of board that we could use, additionally, I wanted to make a unique shape for my board that tends to be a popular shape for small desings that need to be mounted.

The large 1206 capacitors were placed on the back side of the board as they are quite bulky and left very little room for other components on the board. This board features 2-layers with ground pours on each layer, as well as stitching vias to help further with noise.

Assembly

Testing

Notes