1. Circuits from RF to Bits EE194
Brad Wheeler

2. Block Diagram RF gain Down-conversion Signal processing
Noise reasons
Down-conversion
Easier to build low frequency circuits
Signal processing
More gain, filtering
Digitization/demodulation
Extract the information

3. To LNA or Not to LNA? Low Noise Amplifier (LNA) provides RF gain
LNA Design Recipe
Start with common source/gate
Add inductors
Burn lots of current
Pros
Lower Noise Figure
Better sensitivity
Cons
Power consumption
Razavi, Behzad, and Razavi Behzad. RF microelectronics. Vol. 2. New Jersey: Prentice Hall, 1998.

4. Matching Networks
Achieve RF gain using LC resonance instead of active elements
Topologies
L, Pi, tapped element
Metrics
Gain
Must account for loading
Input impedance
Bandwidth
Tuning
Noise
Cr: Prof Niknejad, EE142

5. Matching Network Gain Series to parallel transformation
𝐺𝑎𝑖𝑛= 𝑍 ℎ𝑖𝑔ℎ 𝑍 𝑙𝑜𝑤 −1
Loaded vs unloaded
Realistic on-chip inductors
Q ~
L ~ pH to nH (10nH roughly 200um*200um)

6. Matching Network Gain
Unloaded

7. Matching Network Gain
Unloaded
Loaded, Q=15

8. Down-Conversion Mixers
Move signal from RF (GHz) to Intermediate Frequency (MHz)
Metrics
Input impedance
Gain
Noise
Linearity
Passive vs Active
Razavi, Behzad, and Razavi Behzad. RF microelectronics. Vol. 2. New Jersey: Prentice Hall, 1998.

9. Passive Mixers Input impedance Noise Gain Sinc(Duty Cycle)
Razavi, Behzad, and Razavi Behzad. RF microelectronics. Vol. 2. New Jersey: Prentice Hall, 1998.

10. Passive Mixers Transparency Andrews/Molnar Cook/Berny N-path filter
Limited by Ron/Rs
Andrews/Molnar
Hard switching, multiple phases
Cook/Berny
Resonant, sinusoidal drive

11. Hard Switching Rail to rail switch drivers
Multiple clock phases, non-overlapping inputs
Higher performance, higher power to drive
Andrews, Caroline, and Alyosha C. Molnar. "Implications of passive mixer transparency for impedance matching and noise figure in passive mixer-first receivers." IEEE Transactions on Circuits and Systems I: Regular Papers 57.12 (2010):

12. Sinusoidal Drive
Can also resonate out switch gate capacitance in LC tank
Sinusoidal waveform yields approximately square conduction cycle
Lower LO power, but fewer phases available
Cook, Ben W., et al. "Low-power 2.4-GHz transceiver with passive RX front-end and 400-mV supply." IEEE Journal of Solid-State Circuits 41.12 (2006):

13. Receiver Components RF gain Down-conversion Signal processing
Noise reasons
Down-conversion
Easier to build low frequency circuits
Signal processing
More gain, filtering
Digitization/demodulation
Extract the information

14. IF Amplifiers Direct conversion vs heterodyne
DC offsets, flicker noise
We need amplifiers/filters in the MHz range
First active amplifier becomes the noise vs power limiting factor

15. Filters Why filter? More options than Baskin Robbins
Interference
Noise
More options than Baskin Robbins
Discrete time (DT) vs continuous time (CT)
Aliasing
Active vs passive

16. CT Filters Tow-Thomas Biquad Active Ladder Filter
Passive Ladder Filter
Gm-C Filter
Cr: Prof Boser, EE240C

17. Filter Frequency Ranges
Cr: Prof Boser, EE240C

18. (Active) Switched Capacitor
Transfer function set by clocks, capacitor ratios
Very precise control
Active = Charge being pushed around by opamps
Cr: Prof Boser, EE240C

19. Passive Switched Capacitor
Transconductor converts input to charge
Passive charge sharing defines filtering
Poles determined by capacitor ratios
𝑄𝑖𝑛= 𝑔𝑚∗ 𝑉 𝑖 𝑑𝑇
𝑔𝑚 𝑓 𝑠 𝐶 𝑠𝑖𝑛𝑐 π 𝑓 𝑓𝑠
𝐻(𝑧)
Continuous time gain and anti-alias filtering
Discrete time filtering
Tohidian, Massoud, Iman Madadi, and Robert Bogdan Staszewski. "Analysis and design of a high-order discrete-time passive IIR low-pass filter." IEEE Journal of Solid-State Circuits 49.11 (2014):

20. High Order Poles One transconductor, many switches and caps
Can only implement poles on the real axis with this topology
Tohidian, Massoud, Iman Madadi, and Robert Bogdan Staszewski. "Analysis and design of a high-order discrete-time passive IIR low-pass filter." IEEE Journal of Solid-State Circuits 49.11 (2014):

21. Complex Conjugate Poles
Negative feedback allows to move poles off real axis
Limited to low quality factor
Invert Polarity
Lulec, Sevil Zeynep, David A. Johns, and Antonio Liscidini. "A simplified model for passive-switched-capacitor filters with complex poles." IEEE Transactions on Circuits and Systems II: Express Briefs 63.6 (2016):

22. Complex Filters
By combining charge from In-phase and Quadrature samples, can make filters asymmetric about 0 Hz
Madadi, Iman, Massoud Tohidian, and Robert Bogdan Staszewski. "Analysis and design of I/Q charge-sharing band-pass-filter for superheterodyne receivers." IEEE Transactions on Circuits and Systems I: Regular Papers 62.8 (2015):

23. Passive FIR #𝐶𝑎𝑝𝑠= 𝑁+1 𝑁+2 2 −1 #𝑆𝑤𝑖𝑡𝑐ℎ𝑒𝑠=4∗#𝐶𝑎𝑝𝑠
#𝐶𝑎𝑝𝑠= 𝑁+1 𝑁 −1
#𝑆𝑤𝑖𝑡𝑐ℎ𝑒𝑠=4∗#𝐶𝑎𝑝𝑠
Cook, Benjamin W., and Axel D. Berny. "Passive discrete time analog filter." U.S. Patent No. 8,849, Sep

24. Previous Filter Design
Cascade of IIR & FIR blocks
4th order filter centered at 2.5MHz with Fs = 100 MHz
1-bit zero crossing demodulator
High sampling frequency
Gain requirements
Offset cancellation
(Simulated)

25. ADC/Comparator
Sample rate, number of bits, etc driven by system level modeling
Filter type/passband
Demodulator
Simplest ADC is just a comparator (1-bit)
Demodulate FSK by counting time between zero crossings of square wave

26. Clocked Comparators Strongarm Double Tail
Razavi, Behzad. "The StrongARM Latch [A Circuit for All Seasons]." Solid-State Circuits Magazine, IEEE 7.2 (2015):
Schinkel, Daniel, et al. "A double-tail latch-type voltage sense amplifier with 18ps setup+ hold time." Solid-State Circuits Conference, ISSCC Digest of Technical Papers. IEEE International. IEEE, 2007.

27. Design Considerations
Power, offset, speed, noise
Lower offset either by up-sizing input devices, or by adding correction
Both cost more power
Pelgrom, Monte Carlo
Offset calibration schemes
Current tuning
Capacitor DAC
Body bias

28. Simulation Issues
Switched capacitor circuits require special simulation techniques
Periodic Steady State (PSS)
Compute a solution around a time varying operating point
Periodic Versions of all the normal analysis
PAC
PNoise