System Test Measurements with DC-DC Converters Katja Klein 1. Physikalisches Institut B RWTH Aachen University Tracker Upgrade Power Task Force November 24th, 2008

System Test Measurements with DC-DC Converters Caveat Results are obtained with the APV25. Other front-end chips might behave differently. Not all effects are fully understood. This is work in progress. Katja Klein System Test Measurements with DC-DC Converters

System Test Measurements with DC-DC Converters The APV25 f = 1/(250nsec) = 3.2MHz Katja Klein System Test Measurements with DC-DC Converters

System Test Measurements with DC-DC Converters The APV25 1.25V 2.5V * * is connected to 2.5V since about 2000 Katja Klein System Test Measurements with DC-DC Converters

System Test Measurements with DC-DC Converters The APV25 1.25V 2.5V Katja Klein System Test Measurements with DC-DC Converters

On-Chip Common Mode Subtraction 128 APV inverter stages powered from 2.5V via common resistor (historical reasons)  mean common mode (CM) of all 128 channels is effectively subtracted on-chip Works fine for regular channels which see mean CM CM appears on open channels which see less CM than regular channels CM imperfectly subtracted for channels with increased noise, i.e. edge channels pre-amplifier inverter V250 V250 R (external) V125 vCM strip vIN+vCM vOUT = -vIN VSS Node is common to all 128 inverters in chip Katja Klein System Test Measurements with DC-DC Converters

System Test Measurements with DC-DC Converters System Test Setup TEC petal with InterConnect Board Four ring-6 modules powered & read out Petal housed in grounded metall box Optical readout Optical control communication Thermally stabilized at +15°C Final components (spares) Official DAQ software 6.4 6.3 6.2 6.1 Katja Klein System Test Measurements with DC-DC Converters

Definitions and Analysis Raw (or total) noise = RMS of fluctuation around pedestal value Common mode (CM) = common fluctuation of subset of strips, calculated per APV The raw noise includes the common mode contribution One ring-6 module has four APVs a 128 strips = 512 strips Most tests performed in peak mode Modules are biased with 250V A typical noise distribution { 1 APV Higher noise on edge channels (e.g. from bias ring) Open channels Katja Klein System Test Measurements with DC-DC Converters

System Test with DC-DC Converters Measurements with commercial buck converters with internal ferrite-core inductor Katja Klein System Test Measurements with DC-DC Converters

Commercial Buck Converter EN5312QI Enpirion EN5312QI: Small footprint: 5mm x 4mm x 1.1mm High switching frequency: fs  4 MHz Unfortunately modest conversion ratio (r): Vin = 2.4V – 5.5V (rec.) / 7.0V (max.) Most measurements done with Vin = 5.5V  r(2.5V) = 0.45; r(1.25V) = 0.23 Sufficient current: Iout = 1A Integrated planar inductor Internal inductor in MEMS technology Katja Klein System Test Measurements with DC-DC Converters

Integration into TEC System 4-layer adapter PCB (W. Karpinski) Plugged between Tracker End Cap (TEC) motherboard and FE-hybrid 2 converters provide 1.25V and 2.5V for FE-hybrid Input and output filter capacitors on-board standard caps; low ESR caps tested later, no improvement Input power external or via TEC motherboard Katja Klein System Test Measurements with DC-DC Converters

Integration into TEC System L-type: Larger flat PCB,1 piece TEC motherboard (InterConnect Board, ICB) Front-end hybrid S-type: Smaller inclined PCB, 2 pieces Katja Klein System Test Measurements with DC-DC Converters

Voltage Ripple (L Type) Without load: With load (I = 0.7A): Vin = 6V Vin = 6V High frequency ringing 50mV V2.50 V2.50 10mV Ripple with switching frequency V1.25 V1.25 10mV 200ns  100mVpp high frequency ringing on input  10mVpp ripple with switching frequency on output Katja Klein System Test Measurements with DC-DC Converters

System Test Measurements with DC-DC Converters Frequency Spectrum Standardized EMC set-up to measure Differential & Common Mode noise spectra (similar to set-up at CERN) PS Line impedance stabilization network Load Load Spectrum analyzer Spectrum Analyzer Copper ground plane Current probe Enpirion 2.5V at load Common mode Enpirion 2.5V at load Differential Mode fs Katja Klein System Test Measurements with DC-DC Converters

Raw Noise with DC-DC Converter  No converter  Type L  Type S Pos. 6.4  No converter  Type L  Type S Pos. 6.4 Pos. 6.4  No converter  Type L  Type S Raw noise increases by up to 10% Large impact of PCB design and connectorization Broader common mode distribution Most optimization studies performed with L Katja Klein System Test Measurements with DC-DC Converters

Raw Noise on Different Positions  No converter  Type L  Type S Pos. 6.2 On position 6.1 type L does not fit Preliminary  No converter  Type L  Type S  No converter  Type L  Type S Pos. 6.3 Pos. 6.4 Preliminary Preliminary Katja Klein System Test Measurements with DC-DC Converters

PCB Layout & Connectorization ---- No converter ---- L type ---- S type Pos. 6.4  Some variation within types, but L and S are clearly different ---- No converter ---- L type with S-connector ---- Worst S type ---- Best S type Mean = 1.92548 Mean = 2.08891  = 0.0314997  = 0.0340944 Pos. 6.4  Indication that difference comes from impedance of “bridge“ connector Katja Klein System Test Measurements with DC-DC Converters

Edge Channels with DC-DC Converters On-chip CM subtraction: “real“ CM, i.e. before subtraction, visible on open and edge channels Huge increase of noise at module edges and open strips with DC-DC converter This indicates the real CM Pos. 6.4  No converter  Type L  Type S Katja Klein System Test Measurements with DC-DC Converters

System Test Measurements with DC-DC Converters Module Edge Strips V125 V250 VSS=GND APV25 pre-amplifier [Mark Raymond] strip bias ring connect to V125 Edge strips are capacitively coupled to bias ring Bias ring is AC coupled to ground If V125 is noisy, pre-amp reference voltage fluctuates against input Bias ring AC-coupled to V125  strip and pre-amp reference fluctuate together, lower noise [Hybrid] Katja Klein System Test Measurements with DC-DC Converters

Comparison between Supply Voltages  No converter L10 L11 L10, 1.25V from converter L11, 2.5V from converter zoom on edge channels Either 2.5V or 1.25V line powered via converter; other line powered normally Overall noise increases when converter powers 2.5V 1.25V powers ~only pre-amp; noise on 1.25V subtracted by CM subtraction 2.5V used also after inverter stage; this contribution cannot be subtracted Edge strip noise increases more if converter powers 1.25V Katja Klein System Test Measurements with DC-DC Converters

System Test Measurements with DC-DC Converters Cross-Talk Adjacent modules powered with EN5312QI converters  study correlations between pairs of strips i, j (r = raw data): corrij = (<rirj> - <ri><rj>) / (ij) Without converters With converters on all positions Pos. 6.4 Pos. 6.4 Strip number Strip number Pos .6.3 Pos .6.3 Correlation coefficient Correlation coefficient Pos .6.2 Pos .6.2 Pos .6.1 Pos. 6.1 Strip number Strip number High correlations only within single modules (= common mode) No cross-talk between neighbouring modules Katja Klein System Test Measurements with DC-DC Converters

Noise vs. Conversion Ratio (Vout/Vin) Vout fixed to 1.25V & 2.5V  change of Vin leads to change of conv. ratio r = Vout / Vin Output ripple Vout depends on duty cycle D (D = r for buck converter): Mean noise per module Pos. 6.4 Type L Typical Vin for system test Mean noise increases for decreasing conversion ratio Katja Klein System Test Measurements with DC-DC Converters

Combination with Low DropOut Regulator Low DropOut Regulator (LDO) connected to output of EN5312QI DC-DC converter Linear technology VLDO regulator LTC3026 LDO reduces voltage ripple and thus noise significantly  Noise is mainly conductive and differential mode Would require a rad.-hard LDO with very low dropout  No converter  Type L without LDO  Type L with LDO, dropout = 50mV Katja Klein System Test Measurements with DC-DC Converters

Other Commercial Converters: MIC3385 Are we looking at a particularly noisy commercial device?  Micrel MIC3385 - fs = 8 MHz - Vin = 2.7–5.5 V - footprint 3 x 3.5 mm2  No converter  Enpirion L-type  Micrel L-type  No evidence that EN5312QI is exceptionally noisy Katja Klein System Test Measurements with DC-DC Converters

System Test with DC-DC Converters Measurements with commercial buck converters with external air-core inductor Katja Klein System Test Measurements with DC-DC Converters

External Air-Core Inductor Enpirion EN5382D (similar to EN5312QI) operated with external inductor: Air-core inductor Coilcraft 132-20SMJLB; L = 538nH Ferrite-core inductor Murata LQH32CN1R0M23; L = 1H From data sheet Air-core inductor Ferrite-core inductor 10.55mm 6.60mm 5.97mm Katja Klein System Test Measurements with DC-DC Converters

External Air-Core Inductor  No converter  Internal inductor  External ferrite inductor External air-core inductor Ext. air-core inductor + LDO  No converter  Internal inductor  External ferrite inductor  External air-core inductor Pos. 6.2 radiative part conductive part  No converter  Internal ind.  Ext. ferrite ind.  Ext. air-core ind. Pos. 6.3 (Conv. is on 6.2) Huge wing-shaped noise induced by air-core inductor, even on neighbour-module Conductive part increases as well Both shapes not yet fully understood LDO leads only to marginal improvement Katja Klein System Test Measurements with DC-DC Converters

System Test Measurements with DC-DC Converters Correlations corrij = (<rirj> - <ri><rj>) / (ij) APV 4 Per APV: two halfs of 64 strips strips within each half are highly correlated (90%) but two halfs are strongly anti-correlated (-80%)  linear, see-saw like CM 50% correlations also on module 6.3 (no converter) Pos. 6.4 (with conv.) Pos. 6.3 (no conv.) Katja Klein System Test Measurements with DC-DC Converters

Radiative Noise from Air-Core Coil Module “irradiated“ with detached converter board Mean noise of 6.4 [ADC counts] Reference without converter Increase of mean noise even if converter is not plugged  noise is radiated Noise pick-up not in sensor but close to APVs Katja Klein System Test Measurements with DC-DC Converters

External Air-Core Toroids  No converter  Solenoid  Wire toroid  Strip toroid Pos. 6.4 Preliminary Toroid wound from copper wire Toroid wound from copper strip As expected, toroid coils radiate less than solenoids Significant improvement already observed with simple self-made toroid coil Katja Klein System Test Measurements with DC-DC Converters

Shielding the DC-DC Converter Enpirion with air-core solenoid wrapped in copper or aluminium foil Skin depth at 4MHz: Cu = 33m; Al = 42m No further improvement for > 30m, thinner foils should be tried No diff. betw. floating / grounded shield  magnetic coupling Shielding increases the material budget Contribution of 3x3x3cm3 box of 30m Al for one TEC: 1.5kg (= 2 per mille of a TEC)  No converter  No shielding  30 m aluminium  35 m copper No converter  Copper shield  Aluminium shield Katja Klein System Test Measurements with DC-DC Converters

System Test Measurements with DC-DC Converters Distance to FE-Hybrid  No converter  Type L  Type S‘ Type S‘ + 1cm Type S‘ + 4cm The distance between converter and FE-hybrid has been varied using a cable between PCB and connector Sensitivity to distance is very high Conductive noise is decreased as well due to filtering in the connector/cable Place converter at substructure edge? Pos. 6.4 Type L with Solenoid Type S‘ with Solenoid Type S‘ 4cm further away Katja Klein System Test Measurements with DC-DC Converters

Combination of Measures zoom on edge channels Can get as good as without converter when toroidal coils are shielded and combined with an LDO. Katja Klein System Test Measurements with DC-DC Converters

System Test Measurements with DC-DC Converters Summary and Worries With DC-DC converters powering the APV25, noise is an issue: noise ripple on power lines (conductive) rapidly varying magnetic near field (radiative) Possible countermeasures: Filtering: low pass, LDO, CM filter Shielding Distance A clever combination of these countermeasures will probably work These countermeasures add complexity, cost, mass to the system Noise-tolerant design required for FE-chip, hybrids, PCBs; DC-DC conversion does NOT factorize from remaining system Noise performance should be robust and should scale with system size Katja Klein System Test Measurements with DC-DC Converters

System Test Measurements with DC-DC Converters Back-up Slides Katja Klein System Test Measurements with DC-DC Converters

System Test with DC-DC Converters Measurements with custom DC-DC converters Katja Klein System Test Measurements with DC-DC Converters

The CERN SWREG2 Buck Converter Single-phase buck PWM Controller with Int. MOSFET dev. by CERN (F. Faccio et al.) HV compatible AMI Semiconductor I3T80 technology based on 0.35 m CMOS Many external components for flexibility PCB designed by RWTH Aachen University Vin = 3.3 – 20V Vout = 1.5 – 3.0V Iout = 1 – 2A fs = 250kHz – 3MHz S. Michelis (CERN) et al., Inductor based switching DC-DC converter for low voltage power distribution in SLHC, TWEPP 2007; and poster 24 at TWEPP 08. Katja Klein System Test Measurements with DC-DC Converters

The CERN SWREG2 Buck Converter PCB located far away from module  only conductive noise measured SWREG2 provides only 2.5V to FE-hybrid Noise increases by about 20% 8-strip ripple structure understood to be artefact of strip order during multiplexing; converter affects readout stages of APV No converter 2.5V via S type 0.60 MHz 0.75 MHz 1.00 MHz 1.25 MHz Vin = 5.5V Order in APV after MUX Physical order Katja Klein System Test Measurements with DC-DC Converters

System Test Measurements with DC-DC Converters The LBNL Charge Pump Simple capacitor-based step-down converter: capacitors charged in series and discharged in parallel → Iout = nIin, with n = number of parallel capacitors At LBNL (M. Garcia-Sciveres et al.) a n = 4 prototype IC in 0.35 m CMOS process (H35) with external 1F flying capacitors has been developed (0.5A, 0.5MHz) P. Denes, R. Ely and M. Garcia-Sciveres (LBNL), A Capacitor Charge Pump DC-DC Converter for Physics Instrumentation, submitted to IEEE Transactions on Nuclear Science, 2008. Katja Klein System Test Measurements with DC-DC Converters

System Test Measurements with DC-DC Converters The LBNL Charge Pump Two converters connected in parallel: tandem-converter fs = 0.5MHz (per converter) In-phase and alternating-phase versions Tandem-converter connected either to 2.5V or 1.25V Noise increases by about 20% for alternating phase  No converter  In-phase on 2.5V  Alt-phase on 2.5V Katja Klein System Test Measurements with DC-DC Converters

The Buck Converter (Inductor-Based) The “buck converter“ is the simplest inductor-based step-down converter: Switching frequency fs: fs = 1 / Ts Duty cycle D: D = T1 / Ts Convertion ratio r < 1: r = Vout / Vin = D Can provide relatively large currents (several Amps) Technology must work in a 4T magnetic field  since ferrites saturate at lower fields, air-core inductors must be used Need to find compromise between high efficiency (low fs) and low noise (high fs) Discrete components (coil, capacitors, ...) need space and contribute to material Katja Klein System Test Measurements with DC-DC Converters

The Charge Pump (Capacitor-Based) Step-down layout: capacitors charged in series & discharged in parallel n = number of parallel capacitors Iout = nIin r = 1 / n In → Inductorless technology Everything but capacitors is integrated on-chip  low mass, low space Provides relatively low currents (~ 1A) Fixed “quantized“ conversion ratio (e.g. r = ½) Output voltage cannot be controlled by feedback loop Switching noise Katja Klein System Test Measurements with DC-DC Converters