BCTW calibration status and future Michal Krupa 10/03/2016

M. Krupa BCTW calibration BI/TB WCT internal PCB Beam current path: low impedance, precise matched resistors for symmetry, short traces for good RF performance Calibration path: low DC resistance, high RF impedance to decouple from beam, optimised for calibration with current, symmetry not critical 09/03/2016 M. Krupa BCTW calibration BI/TB

Decoupling calibration from beam Beam signal coupling to the calibration winding introduces an important error to the beam current measurement Minimising the calibration winding current translates to minimising the beam current measurement error Decoupling distributed over the PCB with different ferrite beads covering different frequency ranges (-30 dB @ 40 MHz) 09/03/2016 M. Krupa BCTW calibration BI/TB

Status - calibration of analogue integrators Analogue integrators (DABs) are meant be replaced with the VFC digital acquisition as soon as it is ready Absolute calibration of DABs is very challenging as they measure the bunch integral directly The same procedure as last year: relative calibration with the least effort and cross- calibration with the DCCTs for absolute scaling 09/03/2016 M. Krupa BCTW calibration BI/TB

Status - calibration of analogue integrators Bench top signal generator installed in UA47 connected to the three installed WCTs in parallel Calibration signal is a 5 µs square pulse The generator can be triggered from the DABs The generator can be controlled remotely over ethernet 09/03/2016 M. Krupa BCTW calibration BI/TB

Future - calibration of digital integrators The digital integrators digitise the signal level and compute the integral Only the amplitude needs to be calibrated, timing is intrinsic Precise calibration is possible only with a current source – independence of the cable and load impedances Precise current sources are typically feedback systems – only slow pulses (tens of µs) possible Averaging can be used to increase precision and lower the noise influence 09/03/2016 M. Krupa BCTW calibration BI/TB

Calibration by current To maintain a reasonable calibration current dynamic range and to reduce the power dissipated on the WCT PCBs, low load is essential Signal path is very well defined – a single and separate cable pulled to each of the monitors Long pulses look like DC – no capacitive current leakage, only well defined galvanic connections IDEA: use the same current source to calibrate all WCTs 09/03/2016 M. Krupa BCTW calibration BI/TB

BCTW calibration circuit Current source: ~10 ppm shot-to-shot stability ~100 ppm accuracy ~5 µs switch-on time ICAL limited by VCAL (~1.5 A for RCAL ~ 10 Ω) RREF: 5 Ω ± 0.01% < 0.2 ppm/oC 09/03/2016 M. Krupa BCTW calibration BI/TB

BCTW calibration circuit Current measurement: Half-bridge principle Variable reference voltage source controlled by potentiometer and DAC (coarse / fine) RREF: 10 Ω ± 0.01% < 0.2 ppm/oC RHB: 100 kΩ ± 0.01% < 1 ppm/oC 09/03/2016 M. Krupa BCTW calibration BI/TB

BCTW calibration circuit First prototype / proof-of-concept 09/03/2016 M. Krupa BCTW calibration BI/TB

BCTW calibration circuit Trigger options: Internal (26-pin connector) External (2x SMA) Pulse defining the length of the output current pulse Edge triggering a pulse of one of the predefined lengths WCT PCBs protected from excessive power dissipation by hardware limiting the duty cycle to 1% at 20 Hz 09/03/2016 M. Krupa BCTW calibration BI/TB

BCTW calibration circuit Other features: 8 selectable outputs with reflection compensation circuitry Unused WCT calibration inputs terminated Infinite daisy-chain support, multiple calibration currents possible Temperature monitoring, outputs for monitoring reference voltages by an ADC etc. All control through a simple I2C interface 09/03/2016 M. Krupa BCTW calibration BI/TB

BCTW calibration circuit Future: Measurements and optimisation… Some changes to the PCB design Remote control Internal ADC boards for monitoring the reference voltages and the half-bridge measurements 09/03/2016 M. Krupa BCTW calibration BI/TB

M. Krupa BCTW calibration BI/TB Summary Calibration of DABs done the same way as last year Future calibration pulsed current source for the digital acquisition – work in progress 09/03/2016 M. Krupa BCTW calibration BI/TB

Thanks for your attention Questions?