High precision single edge capture and delay measurement circuit
View Patent ↗A method and circuit for providing on-chip measurement of the delay between two signals includes first and second delay chains ( 241, 242 ) having different delay values connected to sampling latches ( 222 - 227 ) which each include a data input coupled between adjacent delay elements of the first delay chain and a clock input coupled between adjacent delay elements of the second delay chain, thereby capturing a high precision delay measurement for the signals.
1. A circuit comprising:
a plurality of delay measurement circuits connected in a ring oscillator configuration, each delay measurement circuit comprising:
a first chain of delay elements connected to receive a first signal from an on-chip circuit component, where each delay element in the first chain has a first delay value;
a second chain of delay elements connected to receive a reference clock signal, where each delay element in the second chain has a second delay value that is different from the first delay value; and
a plurality of sampling latches connected between the first and second chains, each sampling latch having a data input coupled between adjacent delay elements of the first chain and a clock input coupled between adjacent delay elements of the second chain such that an edge transition in the first signal is indicated by digital values stored in the plurality of sampling latches when the edge transition relative to the reference clock signal occurs within a predetermined measurement window of the circuit; and
a frequency mixer comprising a first input coupled to receive an output from the first chain of delay elements of the last delay measurement circuit connected in the ring oscillator configuration to measure a data ring oscillator period, a second input coupled to receive an output from the second chain of delay elements of the last delay measurement circuit connected in the ring oscillator configuration to measure a clock ring oscillator period, and a frequency mixer output, where the output from the first chain of delay elements has a data ring frequency f D ) from the data ring oscillator period, and where the output of the second chain of delay elements has a clock frequency f C representing an inverse of the clock ring oscillator period, such that the frequency mixer combines the data ring frequency f D and the clock ring frequency f C to generate a mixer output signal at the frequency mixer output.
2. The circuit of claim 1 , where the first chain of delay elements in each delay measurement circuit comprises a first multi-tap delay chain of delay buffers connected in series to receive the first signal, and the second chain of delay elements in each delay measurement circuit comprises a second multi-tap delay chain of delay buffers connected in series to receive the reference clock signal that is asynchronous with the first signal.
3. The circuit of claim 2 , where the second multi-tap delay chain has a per tap delay that is different from a per tap delay of the first multi-tap delay chain.
4. The circuit of claim 3 , where a difference between the per tap delay of the second multi-tap delay chain and the per tap delay of the first multi-tap delay chain provides a measurement precision of the circuit.
5. The circuit of claim 1 , where each delay element in the first and second chains comprises:
a first inverter chain connected to receive an input at an input port and to generate a first delayed version o f the input at an output port; and
a second inverter chain connected to the output port for generating a second delayed version of the input as a tap output that is isolated from the output port and connected to one of the plurality of sampling latches.
6. The circuit of claim 1 , where the plurality of sampling latches comprises a plurality of flip-flop devices.
7. The circuit of claim 1 , further comprising a clock signal generator for generating the reference clock signal which is independent and asynchronous to the first signal.
8. The circuit of claim 1 , where the plurality of sampling latches provides a digital sample of one or more edge transitions in the first signal relative to the second signal when the edge transition occurs within a minimum resolution d of the circuit,
9. The circuit of claim 1 , further comprising:
a first inverter for feeding back the output from the first chain of delay elements of the last delay measurement circuit connected in the ring oscillator configuration to a first input to the plurality of delay measurement circuits connected in the ring oscillator configuration; and
a second inverter for feeding back the output from the second chain of delay elements of the last delay measurement circuit connected in the ring oscillator configuration to a second input to the plurality of delay measurement circuits connected in the ring oscillator configuration.
10. The circuit of claim 1 , further comprising:
a filter connected to filtering the mixer output signal to pass only a difference between the data ring frequency and the clock ring frequency (|f D −f C |), thereby generating the minimum precision measurement d for the circuit.
11. A method for calibrating an on-die measurement circuit comprising , first and second multi-tap delay chains connected to a chain of capture latches such that tap points of the first multi-tap delay chain are respectively connected to data ports of the capture latches and tap points of the second multi-tap delay chain are respectively connected to clock ports of the capture latches, where the second multi-tap delay chain has a per tap delay that is different from a per tap delay of the first multi-tap delay chain, comprising:
connecting the first multi-tap delay chain in series with a plurality of delay measurement circuits in a first ring oscillator configuration to measure a data ring oscillator period;
connecting the second multi-tap delay chain in series with the plurality of delay measurement circuits in a second ring oscillator configuration to measure a clock ring oscillator period; and
computing a minimum precision measurement d for the on-die measurement circuit as a function of a difference value between the clock ring oscillator period and data ring oscillator period.
12. The method of claim 11 , where computing the minimum precision measurement d comprises:
applying an output from the first multi-tap delay chain and an output from the second multi-tap delay chain to a frequency mixer, where the output from the first multi-tap delay chain has a data ring frequency f D from the data ring oscillator period, and where the output of the second multi-tap delay chain has a clock ring frequency f C representing an inverse of the clock ring oscillator period, such that the frequency mixer combines the data ring frequency f D and the clock ring frequency f C into a mixer output signal;
filtering the mixer output signal to pass only a difference between the data ring frequency and the clock ring frequency (|f D −f C |), thereby generating the minimum precision measurement d.