Software Defined Radio Subsystem: RX Quadrature Mixer
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Software Defined Radio Subsystem: RX Quadrature Mixer

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hardware design
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As apart of our second year hardware design course ECE295, our team simulated, designed, brought up, and validated a quadrature mixer as apart of a larger SDR system. View our final presentation here, and our GitHub with all the SCPI/PyVisa testing here.

Electronic Design

Prior to any schematic work, thorough discussion, SPICE simulation, breadboarding took place before finalizing design decisions. Our team’s goal with this project was to maximize performance and simplicity in bring-up/testing with no regard for cost. Hence, our team had a hefty budget of $180 CAD.
 
The high level systems architecture of our team’s design. Schematics available upon request.
The high level systems architecture of our team’s design. Schematics available upon request.
 
From concept to product: bring up!
From concept to product: bring up!
Breadboarding our second order active filter and amplifier.
Breadboarding our second order active filter and amplifier.
Bode plot of the filter/amplifier response.
Bode plot of the filter/amplifier response.

Challenges

Aside from our team’s extremely high power draw, we faced a few setbacks.

Thermals

With our mixer IC hitting almost 80C at peak loads, we had to chose to bias the performance via a current limiting resistor, or something else. In the end, we went with a large heatsink as per our thermal analysis and consistent airflow to drop the internal temperature by 40C.
Chonky heatsinks.
Chonky heatsinks.
Thermal camera shots at peak loads.
Thermal camera shots at peak loads.

Inverting Charge Pump IC

Our inverting charge pumps that supply two -5V rails to each mixer IC (split between rails due to high current draws) required its output to be shorted to ground each time upon start-up. This is a result of a small positive voltage on the output, and is an inherent, known issue with the IC.
 
Manual start-up procedure, featuring our highly unnecessary backlit PCB.
Manual start-up procedure, featuring our highly unnecessary backlit PCB.

Conclusion

Despite minor setbacks, our team won an honourable mention and was able to exceed the requirements for system-level integration, as pictured on the right.
notion image
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