[Homemade Quantum Computer NMRQCP] Completed After Much Trial and Error! The Analog Receiver Circuit

*Original Japanese version is available here.

 Hello! I'm a KOSEN student taking on the challenge of developing a quantum computer using a homemade Earth's Field NMR (EFNMR) system.

This time, I will share the completion of the "analog receiver circuit," which is designed to amplify the extremely faint "FID signal" captured by the coil to a level that can be analyzed on a PC, along with the results of its power-on test.

Completed After Much Trial and Error! The Analog Receiver Circuit

First, building the circuit. For the core, I used the ultra-low distortion, ultra-low noise operational amplifier "AD797BRZ," which I had previously painstakingly converted to DIP (using a breakout board), and built the amplification circuit on a breadboard (EIC-102BJ).

Because this circuit is extremely delicate and complex, putting it together on a breadboard through trial and error was really tough.

What I paid particular attention to was noise reduction. To amplify minute signals without distortion, I carefully incorporated film capacitors, such as "1μF 100V metallized polyester film capacitors," for coupling and noise suppression in the design.

A "Perfect Waveform" Appeared on the Oscilloscope

With the circuit complete, it was finally time to turn on the power and measure the output with a portable oscilloscope.

Look at the screen! Without being buried in noise, I was able to confirm a clean sine waveform output with a Vp-p of 8.80mV.

What's even more important is its frequency. The display in the lower left shows approximately 2.04kHz (Freq: 2.04KHz). This frequency of "about 2kHz" is exactly the band of the "Larmor frequency of protons (hydrogen nuclei) in the Earth's magnetic field," which is the target of this project.

This beautifully proves that the circuit can correctly process and amplify signals in the target frequency band.

Finally, System Integration! The Next Step

Having succeeded in testing this long-pending amplifier circuit, the project finally advances to the final stage.

In the next step, I will physically integrate the "polarization MOSFET circuit" and the "1600-turn sensor coil" I've built so far with this amplifier circuit.

Then, I plan to input the amplified signal into the PC via a "96KHz / 24-bit Hi-Fi USB external sound card" and connect it to the real-time FFT analysis system I created in Python. The moment when hardware and software completely merge is fast approaching!

• Daily experiment notes and code: Available on my GitHub repository (nmr-qc-project)
  
• Real-time development scenes and oscilloscope waveforms: Posting on X (formerly Twitter)
  

If you are wondering things like "Will it really work?" or "How do you generate waveforms?", please bookmark this blog and follow me on X!