Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP TWEPP-07 Topical Workshop on Electronics for Particle Physics TWEPP-07 Topical Workshop on Electronics for Particle Physics Prague 2007 Serial Powering of Silicon Sensors E.G. Villani, M. Weber, M. Tyndel, R. Apsimon Rutherford Appleton Laboratory

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP Outline Serial Powering scheme Characteristics of shunt regulator Experimental results Conclusions

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP P c = I m 2 Rc P M = nI m V m Efficiency:= Example of efficiency plot vs. number of modules (N) vs. number of modules (N) and supply voltage (V) for I m = 2 A R c = 3 Ω for Serial Powering scheme Powering schemes comparison

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP Current source provides power to the chain of shunt regulators. Each of them provides power to the local modules. Communication is achieved through AC coupled LVDS Each sensor has individual HV bias, referenced to its ground ( this might not be necessary) Test structure built and tested with SCT modules Initial stave tests done by C. Haber at LBL Serial powering diagram – module chain shunt regulation -

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP Serial powering diagram – module shunt regulation -

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP Shunt regulator advantageous for steady average current Series regulator can be thought of as a variable resistor in series with a load Series regulator can be thought of as a variable resistor in series with a load Fluctuations in current drawn by the load modifies via the feedback the resistor values : the power supply sees a constant current load, current circulates back into the supply Fluctuations in current drawn by the load modifies via the feedback the resistor values : the power supply sees a constant current load, current circulates back into the supply Shunt regulator can be thought of as a variable resistor in parallel with a load Shunt regulator can be thought of as a variable resistor in parallel with a load Fluctuations in current drawn by the load modifies via the feedback the resistor values : the power supply sees a constant resistance, current does not circulate back into the supply Fluctuations in current drawn by the load modifies via the feedback the resistor values : the power supply sees a constant resistance, current does not circulate back into the supply ∆I ld ↓ Poor isolation ↑ High efficiency ↑ Good isolation ↓ Low efficiency (I loadmax to be provided by the supply) Regulators comparison

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP SPSCT mm x 150 mm SPPCB mm x 83 mm SSPPCB / mm x 9 mm Hybrid SSPPCB ABCD3TV2 Serial powering circuitry evolution

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP Serial powering stave implementation Initial stave work done by C. Haber LBNL

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP Shunt regulator performances The shunt regulator in SSPPCB01 built around standard shunt TL431 Output boosted using PNP D45H8. The output is set to nominally 4V Stability analysis, output impedance Over current condition analysis

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP Phase margin vs. I R esr [0.5, 2.5] Ω I bias decreases phase margin ( g m increases) ESR affects forward feedback compensation ↑ESR OLG CLG Stability analysis

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP Output noise with C1,C3 10  f 16 v ceramic X5R 0805 pack Oscillation bias dependent Tektronix TDS3044B 400 MHZ Stability analysis

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP Output noise with C1,C3 10  f 16 v ceramic low ESR A pack Implication was size of low ESR capacitor ( A pack ) Stability analysis Tektronix TDS3044B 400 MHZ

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP Output Impedance analysis SSPPCB01 Hybrid QL 355 TP I sink AFG3252WR6100A A015 Output impedance and phase measurement Output impedance measured by applying a small sinusoidal varying signal to the driving current by means of a current sink and measuring the corresponding output voltage. From histogram of both peak-to-peak voltage and current the MPV value is determined Their ratio is taken to determine the MPV of output impedance, in the frequency range of 1HZ to 40MHz. From the histogram of the phase difference the output phase delay is measured in the same frequency range.

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP Current and voltage f = 2 and 10MHz Output Impedance analysis

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP SSPPCB01 Shunt regulator output impedance module | Z o | << 1ohm f<1MHz Almost monotonic increase beyond 1MHz Consistent with nominal Open loop gain characteristics of TL431 TL431 open loop gain Output Impedance analysis Ω

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP SSPPCB01 Shunt regulator output impedance phase Arg( Zo) increases ≈ monotonically with frequency Output Impedance analysis degrees Current and voltage output f = 20MHz

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP Low output impedance crucial to achieve good ‘grounding’ and reduce picked up noise Feasible option of using single HV supply for several sensors Output Impedance analysis SR i SR 1 SSSR i SSSR 1

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP Shunt regulator protection analysis The shunt regulator output has to carry the all current in case of load disconnected, to guarantee functioning of the chained modules This condition implies a power dissipation by the shunt device directly proportional to its voltage output thus power wasted and risk of damage if not cooled or over dimensioned A method investigated relies on automatically reducing shunt output voltage in case of overcurrent condition This feature could also be digitally enabled to turn off a module

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP Ibias 500mA Ibias 600mA Thermal analysis of SSPCB01 using IR camera 8…13μm Simulated faulty condition: No clock present onboard No cooling Different biasing conditions (400,500,600)mA * SSPPCB01 was left running at 700mA for 30mins. No change in performances or damaged observed afterwards. Over current condition - Thermal analysis emissivity of Si uncertain, used 0.75

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP Shunt regulator protection scheme The regulator automatically lowers its output voltage (from 4V to 1V in the test circuit) if the current through the power PNP continuously exceeds a set threshold for a set amount of time The voltage output recovers with hysteresis ( ≈ 150mA in the test circuit) The power pulse following an over currernt is not long enough to damage the PNP transistor By proper design the power PNP is housed in SOT23 package, no heat sink needed

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP voltage decreases from 4V to 1V within 3 ms following an over current (40mA to 1500mA) voltage output recovers to 4V from1V (slew rate limited) within 70ms with output voltage 1V the power dissipated by the PNP is ≈ 0.32W. Noise ≈ 2mV circuitry left running for 1.5A. No damage or change in performances seen afterwards. V out I srct Shunt regulator protection analysis

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP Current source SCT4 SP4 SCT3 SCT2 SCT1 SP3 SP2 SP1 Test with up to 6 modules Measure power saving and compare with predicted values Average noise occupancies measured for four ATLAS SCT modules (top and bottom sensor average) Photograph of test setup with 4 ATLAS SCT modules, serial powering scheme implemented on PCB. Test results - SPSCT

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP Test results – SPPCB Average noise (ENC) for six SCT modules powered independently (IP) or in series (SP).

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP Test results - SSPPCB Tests on stave ongoing as modules are fitted One chip not bonded Noise (ENC) for two modules on stave (tests ongoing these days) High voltage biasing scheme comparison: local (left) or shared (right) No differences seen in noise performances

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP Next step – SMARP integrated solution - Power transistor (could be separate die) Linear regulator (optional) DCS including ADCs LVDS buffers Shunt regulator Advantages Avoids matching problems between many parallel regulators Simplifies system and separates functions Allows for cheap MPW run for SMARP  reduce risk and accelerate powering R&D Chips could be used elsewhere (pixels/CMS)

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP Next step – SMARP integrated solution - External serial powering chip Specifications based on experience with discrete solutions and verified by simulations The design could contain additional low voltage amplifiers to implement protection and slow control features Design will contain LVDS section Very generic power chip

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP Conclusions Reliability of Serial Powering demonstrated with several different designs of increasing compactness Crucial advantages of Serial powering in power efficiency, cable, cost and material budget demonstrated Various Serial Powering systems have been running since several years now; understanding of system properties well advanced and constantly progressing Crucial features are dynamic characteristics of shunt regulator Protection schemes devised, designed, built and successfully tested Next crucial step is to design a custom general purpose ASIC (SMARP1), that could be a common ATLAS - CMS supply chip Serial Powering scheme included in the design of future ATLAS SLHC Tracker Strip and Pixel Readout Chip

Rutherford Appleton Laboratory Particle Physics Department G. Villani Σ Powering Prague TWEPP Backup slides – AC coupling Offset C R On-chip Off- chip Multi-drop configuration on stave 1 MHz40 MHz120 MHz