Radio frequency circuits design techniques

First lecture is an introduction to the field of RF, we have not gone through any technical matter (see intro.pdf and intro_EE-426_ICT.pdf).

What is important to remember is the complexity and coexistence of many different standards. Coexistence and spectrum resource allocation with related regulations is a very important point. It's a wonder that up to 7 wireless standards coexist into our phones (NFC, BT/BLE, WiFi, GPS, 4/5G, UWB, basic SAT-COM). There are obviously much more (look at the FCC spectrum allocation between 3kHz to 300GHz)!

ICT has started its revolution 30y ago with www, then 25y 2G/BT/WiFi, 20y camera in our phones, 15y smartphone (app era), 10y BT low energy to prepare earbuds, smartwatch and wearables. ICT is the combo of computing and wireless enabled by integrated circuits and their continuous scaling (1E6 density improvements over 50y) and the cornerstone of the ongoing digitalization revolution (our data to the cloud). LLMs such as ChatGPT are likely another major breakthrough in ICT but all of the above have already completely revolutionized our lives. 

The Friis equation and the min sensitivity one presented at the end are key to remember as they dictate major architectural choices for any comm app. We will revise this at the beginning of next course!

 

We have gone through the first chapter of Enz course (notes included in this week pdf LC_resonant_circuits). In addition you have additional material (lecture notes Chapter 1 Passives, previous week and  Chapter 2, resonant circuits this week if you want to read it for yourself)

You should be familiar with Q definition, transformation between series/parallel equivalent, LC resonant parallel (used in load or shunt elements) and series (typically used along the signal path; an LNA uses both circuits), calculate the Q of a resonant circuit with lossy C and L. L and C do not change much when going from series to parallel or vice versa while RP=Q^2*Rs for Q high enough (Q=10, 1% error, Q=3, 10%).
Understand the link between Q and BW (1/Q). The LNA gain for example with be prop to the Q of the load but its BW will be 1/Q. At 2.4GHz, we have 80MHz BW, this is 3% hence Q should not exceed 30. When taking into account component spread, our resonance (1/LC) will get shifted and we miss the desired band. High-Q desired but be aware of the limits !

With what we learned today you should be capable of designing a simple VCO, calculate its consumption and phase noise. As well you have now almost the skills to design an LNA! We will run examples.

Exercises: Friis and range (in this week's folder, beware of the typo with respect to the exponent which should be negative) and series 1 (Q-factor) located in next week folder. Simon and I will put corrections online ideally before the we !  

Corrections added (this week's folder for Friis/range), see Week 9-15 Oct for Exercices Chapter 1 corrections) 

This week we have covered impedance matching. Lecture notes are to be found in last week's folder (LC_resonant_circuits, 2nd part on Z match, slides) or Chapter 3 (textbook) which you find below.

Smith charts first pages were introduced (Chapter 3) as well, reflection coefficient maps any complex Z along circles. You should be able to place a given Z point on the chart!

You may practice any Z-matching exercises that you find in both lecture notes. Or pick your own, for example at 2.4GHz, with Zin=50 Ohm and Zout= 1kOhm. Calculate the matching network with all types -inverted L, PI/T after you fix the Q (e.g. 10 or try 30 since BW=80MHz @ 2.4GHz), and with the widest possible BW with 2 cascaded inverted-L network. Implement and compare the transfer function of those circuits in Cadence after modifying the example provided in the "Lab tutorial" below which explains how to simulate such a circuit. Try HP/LP version or mixed ones, with and without component reductions (e.g. the L/C in slide 28!) 
There are additional exercises below (exercises chapter 3 part 1 (inverted-L), exercises chapter 3 part 2 (pi-T))

You may compare the results with an ideal L and a real one. Search for Coilcraft or Murata on the web to find the equivalent models (look for high-Q series and choose the component size e.g. 01005, 201, 402, 805 or larger depending on the L value). 
RF Inductors | Coilcraft

LECTURE

1st part

Smith Chart and Impedance matching (Chapter 3 pp 23-36).
You should be able to place any Z or Y on the chart, draw cst Q lines and implement L, pi, T or LL matching and calculate the value of the components from the chart

2nd part

Filter design (Chapter 4 pp

EXERCISES

Reuse examples from the lecture notes (calculated ones) and resolve on Smith chart!

See under next week: exercices_chapter3_part3 and solve the problems 

Check the URL for the online Smith chart simulator, you may add your series, shunt elements, adjust values to implement your matching, add cst Q line (see at the bottom). Watch out, the matching drawing goes from left to right (thus we are looking from the right towards the left). In the lecture note we start from the load (right) and add components towards the source (left). You should thus mirror things horizontally with the online tool (Z black box is that of the load) and you should end up on the Zs* location. Add spread to your components to see how it impacts the final result.   

LTSpice: folder with Z-matching added, copy and practice, compare L, pi and T and low-Q 2L matching networks frequency characteristics, implement some of the course example

1st hour: we have gone through the remaining part of the filter lecture notes. Band pass used in RF or IF, LP for channel selection in baseband. Lecture notes Chapter 4 without the SAW filter section. You should know how to determine the filter order, use filter tables (no need to calculate analytically the components) and do the HP/BP transformation, modify the source, load impedance, simulate and compare different implementations!

The Qorvo whitepaper (not covered) is to give you some hints on BAW acoustic filters. Currently the market is split 50/50 between SAW (surface acoustic wave) and BAW (bulk). No coexistence of radio standards without acoustic filters!

Exercices: implement examples on Cadence, passband, low-pass, high-pass, Chebyshev, Butterworth, with given frequency and input output resistance. Hints: make a parametric model so that you may quickly vary things. Check that your filter is robust against component variations and could be implemented with discrete components (search e.g. for murata or coilcraft RF inductors). 

2nd hour MOS regime of operation, IC factor, small signal equivalent circuit with various conductances (G, S, D). See lecture notes: MOS_Fundamentals from E. Vittoz

We have completed the MOS fundamental parts during the first hour: noise and mismatch. Thus you should be able to replace a transistor with its equivalent small signal circuit and noise source.

Then we have started Chapter 5, up to slides 5.9 included. You should master Friis formula for cascaded F calculation, understand the sensitivity equation derivation that we used in the first lessons to calculate propagation range.   

Exercices: Chapter 5 part 1; F calculation for 2 resistors see word file, done in class! Redo it 1) after adding an impedance transformation network and changing RL to e.g. 1kOhm, what do you conclude?; 2) add a simple common source MOS transistor loaded with a resonant RLC network of your choice and calculate how F is affected when including the transistor thermal noise! Here we keep the 50Ohm physical resistor and make the assumption that any reactive component due to the MOS T is resonated out with an inductor.

FALL BREAK

No lecture notes today! Common source, L-degenerated LNA design discussed on the board! 
For those not attending the class, refer to the corresponding word file. Get familiar with the methodology discussed.
You should be able to replicate this if you are given a different LNA topology. You should know how to calculate voltage and power gain, matching (Zin calc), NF, understand design space and links between components.  

Exercices: finish the design of the LNA including MOS sizing and run it on Cadence, plot Re(Zin), Im(Zin) and verify that it goes to 50 Ohm and 0 Ohm respectively. At first pick a low frequency e.g. 100MHz so that components are big and parasitis negligible. Then repeat e.g. at 2.4GHz. Look at passives on the web (Coilcraft RF high-Q series) to get realistic component values. Safe to use >0.5pF, >10nH! See how adding L1 in series gives you more freedom. Understand what happen when a parasitic cap placed between input and ground affect the circuit (Smith Chart). You should know how to change your design slightly to get back to 50Ohm input!
In Cadence, we will show you how to simulate the NF so that you could compare it with simulations. 
Check the ISPEC ppt file. It explains how to do your sizing for IC=1 (always a good start), knowing gm or current

You may also practice the current conveyor LNA exercice to verify if you master the design technique.

We covered distortion (see lecture notes) and practice cumulated NF and IM3 example building your own EXCEL file

We have covered different RX architectures (see attached lecture notes)

-general considerations: filtering at RF not possible Q would be prohibitive fRF/CHANNEL_BW

-heterodyne: means other frequency, understand how to select channel over entire band with variable frequency local oscillator and convert it to fixed frequency where filtering could be performed, Q relaxes as fIF/fRF; usually with bulky external filters, understand the image problem and the trades-off between image rejection and channel filtering

-homodyne: same frequency (fLO=fRF)->DC, need I&Q down-conversion for FM, phase mod, more amenable to fully integrated solution    

We have completed the architecture slides (discard the last chapter on Software Defined Radio)
We have covered the design of mixers for frequency translation.

Exercises:
Implement SB and DB mixers in Cadence
excel for cumulated NF and IP3 online, see the trade-off between NF and linearity

 

We have studied the implementation of VCOs using vco_ppt_lecture_notes. You also have alternative material from Enz/Dehollain for your own curiosity.

Exercises: derive the phase noise analytical expression as a function of the tank parameters (power of noise / signal power); hint: we consider that noise is split equally between phase and amplitude noise (1/2 factor)

Continuation on VCO design, with material uploaded previously. Understand also VOOs as a FWD and FBCK path as presented at the beginning of Enz lecture notes.

We have gone through Power Amplifier design covering the different classes. Different TX architectures is informative material to be read for yourself if interested.