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. 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. 2Liquid 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 120 Ω resistance in shaper stage C det I in Preamp Multi Gain Shaper Gain Selector Typical input current waveform 3Liquid Argon Week Munich 2011 X1,10,10 0

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

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

Input Stage Q1: minimize series noise Resistor feedback: Prevent interconnect parasitics from increasing 1.25Ω. Large transient feedback currents ~100mA. Input feedback transistor – noise critical! 1mA V CE = 3.6V 0.7mA 9mA V CE = 1.5V V CC2 = 5V V CC1 = 2.5V 6Liquid Argon Week Munich 2011

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

Input Stage Layout considerations: – How to connect to feedback while having minimal impact on resistance ratio? – Low impedance connection to input pad 2R F1 R F2 8Liquid Argon Week Munich 2011

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 600µm 100µm 360µm 60µm 9Liquid Argon Week Munich 2011

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

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

Output driver Wide ground, output connections for low impedance. Minimize potential for current crowding. TopMetal1 (Out) 2R BQ1 400µm TopMetal1 (Out) TopMetal2 (GND) PNP current mirror Q4Q4 Q4Q4 Q 5 (distributed) 12 Liquid Argon Week Munich 2011

Output driver 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) 13 V ce = 3.7V driverIn vc_pnp out 13Liquid Argon Week Munich 2011

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

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

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. 16Liquid Argon Week Munich 2011

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. 17Liquid Argon Week Munich 2011