[help] How to design a RF circuit and debug it?

[czm_88]

As a beginner, i want to know the process and method for RF desing. I don't know how to debug a RF circuit and which parameter should take into account. Is there any basic document to guide a beginner on how to debug a RF circiut?

 

[chihhao]

Some good books can help such as

Razavi,RF Microelectronics
Gonzalez,Microwave Transistor Amplifiers
Pozar,Microwave Engineering

 

[frannk]

Design all components in 50ohm so they can be easily measured.
Make all connecting traces 50 ohms and as short as possible.
Make all vias to gnd as large as possible.
Use the smallest surface mount component(0402) possible.
If you plan on printing inductors or matching networks, avoid using FR4.
Use the smallest value of inductor allowable as collector od drain pull-up.
Simulations should always include connecting traces(pay close attention to trace length on emitters or sources), vias, parasitic inductance of capacitors, parasitic capacitance of inductors.
Shield noisy circuits such as frequency dividers in a PLL.
The list goes on and on....

To trouble shoot, always connectorize each component via good 50 ohm cables to characterize each stage. Avoid using probes at all cost.

 

[yakult]

Hi,

It depends on what circuit you are debugging. For example, if u find the sensitivity of a receiver is not enough. You should consider the RX path. LNA, downconverter and demodulation circuits are included in receiving path. In order to ensure to get enough sensitivity, you should ensure all parts in RX path are work fine. First, you should check the LNA. Critical parameters in LNA are noise figure and gain. If the NF is low enough and gain is high enough, then the LNA is okay. Second, you should check the mixer. If the IP3 and gain (if the mixer is active mixer) are high enough. Then the mixer is okay. Third, check the demodulation circuit, check whether it can demodualte the waveform correctly or not.
Finally, you should check the matching in interstage. Ensure each stage are well matched.

Debugging a RF circuit should be done step by step... I hope it can help u

yakult

 

[brmadhukar]

Hi,
designing is easier compared to building which is easier than debugging.

So while designing take into account the building (implementing) and debugging into consideration. Include parasitics in calculations and also make provision for measurements. Make the measurements with the standard impedances. This will help you in the long run.
Hope it is useful.
B R M