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Calice Meeting – Prague September 12 th 2007 1 Design of a 16 bit DAC for ECAL calibration Status report D. Dzahini, L. Gallin-Martel, O. Rossetto, C. Vescovi Laboratoire de Physique Subatomique et de Cosmologie, Grenoble Theory – modulators –1 st order modulator implementation Design –Modulator –Dynamic Element Matching –SC DAC –SC Filter Conclusion – Remaining tasks

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Calice Meeting – Prague September 12 th 2007 2 16 bits LF 1 to 5 bits HF modulator converter theory oversampling and noise shaping Quantization noise = Signal fe/2-fe/2 Signal BW Signal fe/2 Signal BW quantization noise => noise shaping

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Calice Meeting – Prague September 12 th 2007 3 Signal to Noise Ratio of ideal converters Nyquist rate converters : Oversampled converters : converters : N : number of bit OSR : oversampling ratio k : modulator order with

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Calice Meeting – Prague September 12 th 2007 4 First order modulator DAC implementation (1) ACC Q US U(z) E(z) S(z) (high pass filter) E(z) : quantization noise

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Calice Meeting – Prague September 12 th 2007 5 First order modulator DAC implementation (2) ACC Q US Q U S + DFF CLK A Standard CMOS techno. VHDL implementation The output S can be single or multi-bit.

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Calice Meeting – Prague September 12 th 2007 6 A 16 bit DAC block diagram 16 bits 3rd order 9 level modulator 9 level DEM Diff to Single CT filter 9 level SC DAC Single ended output voltage CLK Offset cancelation 4th order SC filter From pulser

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Calice Meeting – Prague September 12 th 2007 7 A 16 bit DAC 3 rd order, 9 level modulator (1) A 96 dB SNR is necessary to achieve a 16 bit resolution. A 3 rd order, 9 level (3.2 bit) modulator leads to a SNR : 168dB for OSR=256 147dB for OSR=128 => related to the SC filter design (settling time). 126dB for OSR=64 Multi-bit : SC filtering and OPA constraints are relaxed quantization noise is reduced, a DEM is necessary to reduce the DNL effect of the 9 level DAC. The modulator was designed using the Matlab toolbox written by R. Schreier

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Calice Meeting – Prague September 12 th 2007 8 A 16 bit DAC 3 rd order, 9 level modulator (2) U 16 bits Z -1 + + + Q c1 c2 c3 a2 a3 x1 x2 x3 a1 b1 S 4 bits (3.2) VHDL implementation Can also be simulated using C language S=c3*x3; if (S>4) S=4; if (S<-4) S=-4; x3=x3 + c2*x2 - a3*S; x2=x2 + c1*x1 - a2*S; x1=x1 + U - a1*S; Adders overflow is not simulated with this code.

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Calice Meeting – Prague September 12 th 2007 9 A 16 bit DAC Dynamic Element Matching (1) 3 : 2 : 5 : 4 : Data Weighted Averaging (DWA) Random re-mapping turns elements mismatch into white noise. DWA re-mapping shapes DAC errors noise. + DSM 4 4 4 XOR DAC with equal bit-weights 8 8 Thermo D Q

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Calice Meeting – Prague September 12 th 2007 10 A 16 bit DAC Dynamic Element Matching (2)

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Calice Meeting – Prague September 12 th 2007 11 A 16 bit DAC SC DAC Based on Direct Charge Transfer (DCT) : - DAC operation is performed during 1 (capacitor arrays charging) - Charges are shared with the feedback capacitor C during 2 (DCT) - Ref voltage is limited by the OPA dynamic range (linearity) Low pass DCT : Ref+ sum out Ref- 1. DSMi CiCi 22 DSM[7:0] 11 22 11 22 C C out sum out C array

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Calice Meeting – Prague September 12 th 2007 12 A 16 bit DAC SC Filter 11 11 22 11 22 22 11 22 22 11 22 11 11 4th order, SC direct implementation of a MFB Butterworth Filter (Fc = 2kHz) - Two 2 nd order filter cascaded - Two differential OPA

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Calice Meeting – Prague September 12 th 2007 13 A 16 bit DAC Differential OPA (1) The OPA used in the SC DAC and in the SC Filter was designed (D. Dzahini) to be implemented in 12 bit, 25MHz ADCs. The main features of this OPA are : - Open loop gain : 100dB - Gain-band product :130MHz - Dynamic range :1.6V - Power consumption :6mW (3 instances required => 18mW) Simulations have to be carried out to reduce the power consumption.

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Calice Meeting – Prague September 12 th 2007 14 A 16 bit DAC Differential OPA (2)

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Calice Meeting – Prague September 12 th 2007 15 A 16 bit DAC Remaining tasks A first prototype will be submitted to the January 2008 run - Simulations have to be carried out to complete the SC filter design : filter topology & response OPA power consumption - The output stage has to be designed : differential to single ended converter (if implemented in the 1st proto) CT filter (if implemented in the 1st proto) output buffer (s) - Pulser & Offset cancellation : ? Pulser specification and design (who ?) The modulator has an offset cancellation capability, its control depends on the pulser design.

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