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Barrel EM Calorimeter Preamp / Shaper Update

Barrel EM Calorimeter Preamp / Shaper Update. Mitch Newcomer, Andrew Townley Prepared for Munich Liquid Argon Week 2011. Status April 2011. Installed IHP’s Cadence IC6 design tools. Some issues identified with PDK but mostly OK.

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Barrel EM Calorimeter Preamp / Shaper Update

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  1. Barrel EM Calorimeter Preamp / Shaper Update Mitch Newcomer, Andrew Townley Prepared for Munich Liquid Argon Week 2011

  2. Status April 2011 • Installed IHP’s Cadence IC6 design tools. Some issues identified with PDK but mostly OK. • A Preamp Design and layout is near completion in IHP’s SG25H3P ( Complementary Bipolar process ). • Alternative Preamp configurations are being considered for layout. • Discussion underway with IHP to collaborate on measurements of their PNP devices. Liquid Argon Week Munich 2011

  3. Design Overview & Constraints • Preamp constraints: • Wide input dynamic range ~70nA – 5mA (16 bit) • Accuracy target 13 bits Present fixed input impedance (25 Ω) across full range • Linear response across input range • Variable detector capacitance • 50pF – 1nF • Able to drive 120Ω resistance in shaper stage Preamp Multi Gain Shaper X1,10,100 Gain Selector Cdet Iin Typical input current waveform Liquid Argon Week Munich 2011 3

  4. Preamplifier • Shaping depends on detector capacitance • Increased Cdet: • Increases tpeak • Reduces output amplitude. • Increases series noise • Net: Increased capacitance -> worse SNR Cdet = 50pF Cdet = 200pF Cdet = 1nF Input current in above: 5mA peak Liquid Argon Week Munich 2011 4

  5. Preamplifier Circuit Ideal Shaping elements Total Preamp Power ~ 45mW Liquid Argon Week Munich 2011

  6. Input Stage VCC2= 5V • Q1: minimize series noise • Resistor feedback: • Prevent interconnect parasitics from increasing 1.25Ω. • Large transient feedback currents ~100mA. 0.7mA VCE = 1.5V 1mA VCC1= 2.5V 9mA VCE = 3.6V Input feedback transistor – noise critical! VCE = 1.5V Liquid Argon Week Munich 2011

  7. Input Stage I(Rgain1) vgain vfollow VCE (Q2) VCE (Q1) 50pF I1 Liquid Argon Week Munich 2011

  8. Input Stage • Layout considerations: • How to connect to feedback while having minimal impact on resistance ratio? • Low impedance connection to input pad 2RF1 2RF1 RF2 Liquid Argon Week Munich 2011

  9. Feedback resistors • Used lowest per-square resistance available • Easiest way to achieve 1.25Ω resistor • Less than one square of resistance • Tradeoff: ~30Ω feedback resistor ends up being very large • Will be some uncertainty in 1.25Ω • Solution: only include 20Ω out of 30Ω on chip • Externally tunable • Split 20Ω into two parallel 40Ω • Avoid current crowding effects 100µm 600µm 60µm 360µm Liquid Argon Week Munich 2011

  10. Input Stage Input transistor Q1 NPN_MV: Nx=8, Ny=1, m=8 12µm TopMetal1 Emitter connection: L=150µm Emitter connection: W=400µm Liquid Argon Week Munich 2011

  11. Feedback resistors Self Heating Resistance Safe Area • RF1, RF2 set input impedance • Need to dissipate ~100mA peak • Also must be of same type (for matching) • Width determined by power density allowance I (mA) • Max density in Rsheet larger than allowed by contact density • Possible to make addt’l contact row?? (1 cont. per 0.75µm) × (0.4mA per contact) = 0.53mA/µm effective max density 0.75 µm Liquid Argon Week Munich 2011

  12. Output driver • Wide ground, output connections for low impedance. • Minimize potential for current crowding. 400µm TopMetal2 (GND) TopMetal1 (Out) Q5 (distributed) 2RBQ1 TopMetal1 (Out) 2RBQ1 PNP current mirror Q4 Q4 Liquid Argon Week Munich 2011

  13. Output driver Vce= 3.7V out • Output driver block • PNP “inverts” voltage signal as current • RC2 converts to voltage • Q5 draws more current (connected to feedback point) • Same function PNP or PMOS? • PNP Vceo Limit (2.5V) • PNP Vcbo (4V) driverIn Vce= 3.7V vc_pnp Liquid Argon Week Munich 2011 13

  14. Output driver • PMOS, not PNP? • Higher Vbreakdown. (3.3V) • Output impedance set by gm of PMOS • Reduces effective overall gain when driving low-impedance of feedback Liquid Argon Week Munich 2011

  15. Output driver • PNP: • Output driver gain 0.96 • PMOS: • Output driver gain 0.73. ( First try) Liquid Argon Week Munich 2011

  16. Chip level • Target: Two or four preamps per chip: PMOS and PNP? • Add test structures in extra space. • Look at breakdown, noise from different transistors. Liquid Argon Week Munich 2011

  17. Summary and Plans • IHP SG25H3P process is relatively expensive and may offer significant advantages. • PNP Vceo of 2.5V vs operating point of 3.2 to 3.7V is the only potential issue identified with the process. Transistor is in a safe operating point but the concern is that spontaneous breakdown currents may occur adding to the amplifier noise. • Plan to submit one or two versions of the preamp in the July 2011 run to understand this issue. • IHP has expressed interest in working in collaborating on measurements of the radiation sensitivity of the IHP PNP transistors. Details are under discussion. Liquid Argon Week Munich 2011

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