Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
John MussonJohn Musson(and Colleagues!)(and Colleagues!)
TJNAFTJNAF
Ultra-Linear ReceiversUltra-Linear Receiversfor Digital LLRF Control Systemsfor Digital LLRF Control Systems
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 2
Receiver Parameters
IntrinsicNoise Figure
Low-end limitUltimate sensitivity
SaturationLarge-signal limitations, distortion
LinearityEverything in-between!
ExternalPhase NoiseADC Sampler JitterInterference ”blocking”Reciprocal mixing
Additionally,AM demod is inherently linearPM is NOT!
Threshold effect
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 3
Taxonomy
IIP3 = Input 3rd Order Intercept Point
P1dB = 1 dB Compression Point
K = Boltzmann's Constant
To = 290 degrees Kelvin
NF = Noise Factor (linear)
F = Noise Figure (in dB)
SFDR = Spurious-Free Dynamic Range
BW = Receiver Bandwidth
MDS = Minimum Discernible Signal
SNR = Signal to Noise Ratio
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 4
All Math Aside....or a Toolbox Smorgasbord
To = 290 K (IEEE)
KTo = -174 dBm
NF = Tsys /290 + 1
F = 10 log NF
IIP3 =
Pim = 3Ptone – 2PIIP3
NFnet =
SFDR3 = 2/3 (IIP3 + 174 – F -10log BW)
SFDR2 = ½ (IIP2 + 174 – F -10 log BW)
Pphase noise = Punwanted + 10log BW + Prx phase noise
SupressionOrder 1
Ptone
F1F2 1
G1F3 1
G2 G1...
Processing Gain 10 logfs
BWx Eff
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 5
Courtesy “RF and Microwave Designer's Handbook, Watkins-Johnson Company, 1997 “Introduction to Radio Frequency Design,” Wes Hayward, ARRL 1994
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 6
499 MHz Warm Cavity Requirements
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 7
Receiver Bandwidth
Software Defined Radios (SDRs) can have 2 associated bandwidths:
AnalogMinimum element in Front EndFactors include latency, anti-alias,
IF / DigitalGenerally the narrowest, set by IIR / FIR
DR Calculations should use the analog BWSNR should use narrow/digital BW
In addition, Closed-Loop control BW for LLRFBW determined largely by sensitivity (KTB) and latency (“Group Delay”) requirementsEx. JLAB LLRF Rx uses a 8 MHz BPF exhibiting 100 ns of latency
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 8
Components
High IIP3 FET MixerWJ HMJ5
IIP3 = 35 dBm
Try to shield active (vulnerable) amplifier, but not deep enough to destroy noise figure!
High IIP2 / IIP3 AmplifierWJ AHJ-2
IIP3 = +26 dBmF = + 4dB
3 6 3
+17 dBm LO
AHJ2HMJ5
BPFBPF
Thermopad
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 9
Don't Forget the ADC!!
Effective Dynamic Range = -1.25 + 6.02b + 10log fs
b = # of bits, fs = sample frequency
1 Hz BW
DR > Analog, and LSB >> MDS
Noise Figure can be assigned
Function of sample rate and # of bits
F = 12 dB (AD 6645 w/ fs = 56 MHz, Rs = 200 Ohms)
S/N degradation from sample clock jitter:
2228 σfopi
fs=
N
S
Reference: Frerking, M., “Digital Signal Processing in Communication Systems”
Sets ultimate PM S/NSets ultimate PM limitSets ultimate PM limit
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 10
Pmin
Courtesy “Digital Signal Processing in Communication Systems,” Frerking, M., Chapman and Hall,1994
“Digital Communications,” Proakis, J., McGraw-Hill, 1994
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 11
Modeling
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 12
Modeling (Dynamic)
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 13
Grouping Relevant Terms.....
Pmin ~ KToB + Fnet + S/Njitter + Pphase noise + S/Nimposed - ??? (ie Processing Gain from DSP decimation??)
JLAB LLRF (Gradient)IF = 70 MHz, fs = 56 MHz, B = 10000 (control BW)
-134 + 35 + (<90 dBc for < 200 ps) + ? + 80 -20 = -39 dBm!!
So, our receiver is within spec at Pin > -39 dBm.
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 14
What About High-End?
FET mixer (IIP3 = +35 dBm) combined with CATV amplifier (IIP3 = +27 dBm), predicts an IIP3 of + 43 dBm (+41 dBm measured)
Maintaining an IM supression of 80 dB implies:
Pmax = 2* 43 – 80 = + 3 dBm.
So, based on the additional requirement of 20 dB of specification compliance, we achieve +3 - (-39) = 42 dB of dynamic range (100 : 1) with 80 dB of supression on either side.
Arguably, high-end range can also be extended by noting that IM corruption is correlated….Would most likely lead to a “DC” phase offset”
Presumption of some processing gain bails us out!!!
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 15
Verification Measurements
• Noise Figure
— Y-Factor
• Effective for F < 25 dB
• Affordable; easily built into receiver front ends
— Spectrum Analyzer + LNA
• Nice paper presented by T. Powers at BIW '98
– “Improvement of the Noise Figure of the CEBAF Switched Electrode Electronics BPM System”
• MDS / Tangential Sensitivity
— Easy to do; outcome-based!
— Can also be built-in
• Dynamic Range
— 1 dB Compression
— IIP3
• Phase Noise
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 16
“Fundamentals of RF and Microwave Noise Figure Measurements,” HP Tech Note 57-1“Noise Figure Measurement Accuracy- The Y- Factor Method,” HP Tech Note 57-2
“Radio Astronomy,” J. Kraus, Cygnus-Quasar, 1988
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 17
Two-Tone IMD Test for IIP3
Courtesy “Improve Two Tone, Third Order Testing,” Mini Circuits Tech Note
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 18
Courtesy “Introduction to Radio Frequency Design,” W. Hayward, ARRL, 1994
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 19
Phase Noise
Or........
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility
Page 20
Summary
• Life for the Analog RF Engineer is STILL interesting!
• Back-to-basics design and testing
—Made much easier with modern ($$) test equipment
—Models are quite reliable for first-cuts
• Narrowband techniques can improve most parameters (ala Genesys)
• If LLRF becomes more demanding…….(?)
• 73, DE WD8MQN
