Presentation on theme: "Cavity BPMs for Happex and G0 John Musson. Triplet Configuration…X, Y, and I TM 010 Mode for I TM 110 Mode for X & Y –Slugs provide proper excitation,"— Presentation transcript:
I & Q Demodulation I Q DE- MO D I @ 28 Msps ADC 70 MHz LO 90 Degree I & Q 56 Msps ADC 0 2 3 1 + 1 COUNTE R RE G ADC70 MHz LO 56 Msps System Clock 14-Bit 2s Complement 0 2 3 1 + 1 RE G Q @ 28 Msps = +I+Q-I-Q+I+Q-I-Q+I+Q-I-Q+I+Q-I-Q+I+Q-I-Q+I+Q
Happex Run BCM Crosstalk Helicity-correlated position differences, vs stripline,1nm Resolution BCM DD Glitches BCM Linearity Helicity-correlated position difference. xtalk Same plot, better data!
Happex Run Bad News….. Limited Dynamic Range –Required external amps and filters Crosstalk…~45 dB of C-C isolation –BCM signal would corrupt X & Y Software Problems –Register overflow resulted in glitching and Bedposts Synchronous Detection => Dedicated MO –Phase noise and distribution issues (LOL) Data COURTESY l. Kaufman, K. Paschke, R. Michaels
In Addition Setup is a learned behavior! –We devised a procedure, which proved to be more difficult than expected with actual beam. Hall personnel eagerly participated….. –More eyes –Technical understanding of benefits and limitations –Fantastic model for future systems
G0 Improvements Hardware –Crosstalk path identified. IF traps installed on Local Oscillator lines => > 60 dB –Amplifier removed from BCM (I) channel –Additional bench testing to understand Software –Register rollover identified, corrected, and tested. MO –Try asynchronous operation, due to large Phase Noise in Halls Hall personnel also system-savvy! –Data courtesy R. Suleiman
Known Improvements 50 nA Sensitivity –Currently have 74 mm resolution! Need additional 37 dB to achieve 1 mm. LNA? –I-cavity is not a problem…plenty of signal Shore up all hardware fixes (ie. LO-IF traps) Firmware and Additional tests. Setup Procedure (EPICS) and All-Save Return to Synchronous MO –Must improve MO Distribution to Hall(s) Cavity Investigation on Downstream X&Y –How can we duplicate beam+cavity behavior in the lab? Thank you to all for data, feedback, and especially patience!
CORDIC Algorithm COordinate Rotation DIgital Computer –Jack E. Volder, The CORDIC Trigonometric Computing Technique, IRE Transactions on Electronic Computers, September 1959 –Ray Andraka, A Survey of CORDIC Algorithms for FPGA Based Computers, FPGA '98. Proceedings of the 1998 ACM/SIGDA sixth international symposium on Field programmable gate arrays, Feb. 22-24, 1998, Monterey, CA. pp191-200. Iterative method for determining magnitude and phase angle –Avoids multiplication and division N bits +1 clock cycles per sample Can also be used for vectoring and linear functions (eg. y = mx + b)
Concept Exploits the similarity between 45 o, 22.5 o, 11.125 o, etc. and Arctan of 0.5, 0.25, 0.125, etc. Multiplies are reduced to shift-and-add operations AngleTan ( )Nearest 2 -N Atan ( ) 451.0145 22.50.4140.526.6 11.250.1990.2514.04 5.6250.0950.1257.13 2.81250.0490.06253.58 1.4061250.02460.031251.79 0.7031250.01230.015630.90
Y X Binary search, linked to sgn(Y) Successively add angles to produce unique angle vector Resultant lies on X (real) axis Functionally..... with a residual gain of 1.6