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QIE10P5 status 1. Digital power-up issue 2. New: power sequencing issue 3. Suggested strategy for impedance issue 4. Submission plans Tom Zimmerman 7/3/13 1. Digital power-up issue At the last meeting, I pointed out a possible ADC encoder bus contention problem, which results in excess supply current upon power-up. I have redesigned the ADC latch as proposed, run simulations, and modified the layout. Ck Power-on-resetb Differential flash ADC latch SIG in REF in + _ 1 + _ 1 + _ 1 compare latch Ckb Ck,Ckb latch Changed this 63 6 encoder I + _ 0 + _ 0 A “1100” transition is encoded 0 to that Working on the digital power-up issue exposed another issue: power sequencing. This was NOT an issue with QIE8, since QIE8 was a single-supply device. QIE10 requires two separate supplies: 3.3V and 5V. Prior to thinking about the digital power-up issue, I had not considered the impact of powering up one supply before the other one. The situation is as follows: if one supply is powered up and the other is still at 0V, then in multiple areas of the chip, certain bipolar transistor voltage ratings are exceeded. In addition, extra current flows from the powered supply into the unpowered supply pin. On the prototype, this has no disastrous effect. However, it can result in long-term reliability issues. This is NOT acceptable. IDEALLY, each supply should be completely independent and either could be powered up or down before the other WITHOUT exceeding any transistor voltage ratings. I have identified all areas (>10!) in which this problem exists and have made appropriate design modifications. The changes have been implemented in the layout. None of these changes are major, but given the number and extent of the changes, I think that another prototype submission is required. A QIE11 prototype submission could in principle verify all the power-up related design changes. Some thoughts on the impedance matching issue It would be preferable to NOT have to program the impedance of each and every chip. The two sources of impedance variation that we cannot avoid are: A. Cable-to-cable variation (measured to be up to 3% across one bunch of 24 cables) B. QIE input impedance variation with signal amplitude: De-biasing problem worst in this range We want to avoid signal reflections, especially large opposite-sign reflections that would de-bias the QIE for many buckets. Possible strategy: Natural increase in impedance helps to avoid opposite sign reflections for moderately big signals Use modified bias: lower power, better impedance profile. Set this impedance with 0.1% external resistors. Set to slightly > 50 ohms to avoid possible opposite sign reflections for the biggest signals. Or, set to exactly 50 ohms and tolerate occasional de-biasing due to infrequent biggest signals. Region 1 Impedance determined by feedback amp bias: Rsetp, supply voltage, temperature, MOS Vth. Region 2 Impedance determined only by external resistors Impedance mismatch doesn’t matter so much in Region 1 since signals are too small to de-bias the QIE. Either tolerate possible mismatch, or program the QIE Region 1 impedance to match the cable. Easy to adjust this impedance with an added DAC. Minimize the impedance variation in Region 1 with an improved biasing scheme: Present scheme Improved scheme Feedback amp bias Internal Isetp DAC External Rsetp Default Current =0 Eliminate this DAC. Originally intended to allow Region 1 impedance tweaking, but not an efficient way to do that. Vbandgap (generated on-chip) = 1.7V Temperature compensation External Rsetp Insensitive to Vsupply, temperature, MOS Vth. Chip pinout does not change, only external resistor value. Internal Iclamp DAC An efficient way to adjust Region 1 input impedance. Leave it at the default or choose to program it. Submissions MOSIS submission dates: 8/26 and 11/11. As of now, the power-up and power sequencing changes have been implemented in a QIE10P5_mod directory. The suggested changes for the impedance issue are not implemented. The QIE11 front end (if shown to work) could be stitched into the QIE10P5_mod layout. This would verify all the powerrelated design changes. Not known if this could be done in time for an August submission – depends on QIE11 front-end testing (starting now). What QIE11 shunt factors are desired?? Not sure yet what is achievable. Preliminary results: the QIE11 prototype is alive and functioning in X1 mode. If QIE11 submission is not possible in August, then should we submit a QIE10 (with impedance design changes implemented)??