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The Chicago Half of Champ
Jean-François Genat, Eric Oberla, Herve Grabas
Jean-François Genat, Eric Oberla, Herve Grabas
04/20/23 13rd Chip Review
Champ Psec Features•Psec – 3 is a test Asic. Will not provide
timing measurement. •Main features :
▫DLL (Delay Locked Loop).▫Free running delay line.▫DLL test structures.
•Test structures:▫Ring oscillator (with new D-Flip Flop).▫Transmission lines.▫Resistors.
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Overall presentation•The DLL will allow us to have a controlled
sampling rate.•Provide us a cleaner sampling window•No dead zone of sampling ( if the effective
delay free running delay line is less than the period of the input clock -> dead time)
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CMOS design
•Cell design Phase detectorCharge pumpDelay lineSome control logic
•SimulationComplicated: long locking time, small time
steps.The use of VerilogA language and mixed
signal simulation saves you.
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DLL simulation•Difficult because:
DLL function with 40ps delays.Locking take up to 100us.
• Therefore, there is more than 7 orders of magnitude of difference between the smallest time step and the biggest one.
• Solution : not simulating the internal function of the delay line.
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Delay line simulation model (1)•Delay line structure: chain of small
delays.
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Generates a sampling frequency equals to Delay
1
Delay line simulation model (2)• From its input and output the delay line is however
nothing else than a big delay adjustable by to voltages : VCN and VCP.
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Delay line simulation (3)•VerilogAMS description of the VCDL:
Allow us to describea variable delay.
Description uses postlayout results from Eric
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DLL simulation success04/20/233rd Chip Review
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Delay Locked Loop principle1. VCN and VCP are set to their max value (1.2 & 0
resp.). The propagation delay in the DLL is then the smallest -
> 11ns.2. The delay is increased until it reaches the delay of
one clock cycle.3. The phase comparator locks then the delay of the
delay line at one clock cycle
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Delay locked loop control logic• In a delay locked loop the generated delay of the delay line
cannot reach 0. It is always minored by the smallest delay of the line. Here 11ns.
• Therefore, the DLL can never lock on the first edge of the clock. (See Fig.)
• However the phase comparator work at ±180° around a clock edge. And in some case this can result in the DLL trying to lock on the first edge of the clock (See Fig.)
• This has to be taken care of. Some simple logic is sufficient.
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DLL control logic (2)
• The control logic outputs 1 if VDLL is in the wrong pull-in range.
• After having being active the pull-out logic is inactivated. (The DLL can only be in the wrong pull-in range once).
• The control logic operates directly on the phase comparator to preserve its speed.
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Dynamic phase comparator04/20/233rd Chip Review
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• It is a dynamic phase comparator so it is extremely fast. Therefore it gives us very accurate jitter correction.
• Adjusted to give us directly the right control signal for the charge pump. (No extra inverted needed).
• Shift logic integrated.
Charge pump
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• High performance charge pump.
• 1uA external current source.
• Cascode current mirror to increase output resistance, so that charging and discharging current are not disturbed by the state of the output. (Better current matching).
Results
•Successful simulation and locking pre and post layout.
•Lock time ~ 10 us.•Simulation time ~10 min.•Measured jitter 300fs in post-layout
simulation with the behavioral model of the DLL (will probably increase in the physical design).
•DLL system is stable and precise.
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Chip layout
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•Submitted to CERN May 31st.
•30 units ordered.
Backup slides
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Delay locked loop04/20/233rd Chip Review
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•Whole schematic circuit with the control logic.
Layout: Charge pump & Phase detector
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•Layout of the charge pump and phase detector done together for better matching and smallest wiring capacitances.
•16um x 18um
Layout Control logic
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Results (2): The pull-out
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Pull-out control signal
Decrease in VCN -> Increase in delay.
Results (3) : The locking
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Small UP and DOWN control signal. Locking almost complete.
Results (4) : The jitter
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Very low delay variations at the output of the delay line
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