Data capture circuit with self-test capability
A data capture circuit having a self-test capability includes a first data capture element to be tested in a self-test mode of operation, at least one additional data capture element, e.g., a second data capture element that is a substantial duplicate of the first, a clock generator circuit, a controller and a comparison circuit. The clock generator circuit is configured to generate a clock signal for application to clock inputs of the data capture elements, and a number of selectable clock-based test data signals. In the test mode, the controller selects at least a particular one of the test data signals for application to a data input of the first data capture element. A delayed version of the selected test data signal is applied to a data input of the second data capture element. The comparison circuit is configured to compare output signals generated by the first and second data capture elements, and supplies a result of the comparison back to the controller. The controller repeats the selection of particular test data signals and monitors corresponding comparison results until set-up and hold times or other clocking characteristics of the first data capture element are determined to a desired level of accuracy.
1. A data capture circuit having a self-test capability, the data capture circuit comprising:
at least first and second data capture elements;
a controller for controllably selecting at least a particular one of a plurality of selectable clock-based test data signals for application to a data input of the first data capture element, a delayed version of the selected test data signal being applied to a data input of the second data capture element; and
a comparison circuit coupled between data outputs of the first and second data capture circuits and an input of the controller, the comparison circuit being configured to compare output signals generated by the first and second data capture elements, a result of the comparison being applied to the controller input;
wherein the controller repeats the controllable selection of particular test data signals and monitors corresponding comparison results until a clocking characteristic of at least one of the first and second data capture elements is determined to a desired level of accuracy.
2. The data capture circuit of claim 1 further comprising a clock generator circuit configured to generate (i) a clock signal for application to a clock input of the first and second data capture elements, and (ii) the plurality of selectable clock-based test data signals.
3. The data capture circuit of claim 1 wherein the first and second data capture elements comprise a pair of flip-flops.
4. The data capture circuit of claim 1 wherein the clocking characteristic comprises at least one of a set-up time and a hold time.
5. The data capture circuit of claim 2 wherein the clock generator circuit comprises a delay lock loop (DLL) having a first output corresponding to the clock signal, and a plurality of additional outputs each corresponding to one of the plurality of selectable clock-based test data signals.
6. The data capture circuit of claim 1 wherein the plurality of selectable clock-based test data signals comprise 2n+1 versions of a divided-by-two clock signal, each having a different amount of delay associated therewith.
7. The data capture circuit of claim 1 wherein the plurality of selectable clock-based test data signals are applied to corresponding inputs of a multiplexer having a control signal input coupled to an output of the controller, the controller selecting a particular one of the test data signals by application of a control signal to the control signal input of the multiplexer.
8. The data capture circuit of claim 1 further comprising a controllable delay element, the controllable delay element having a first input for receiving the selected test data signal, a second input for receiving a control signal from the controller, and an output corresponding to the delayed version of the test data signal.
9. The data capture circuit of claim 1 wherein the plurality of selectable clock-based test data signals are applied to corresponding inputs of each of a first multiplexer and a second multiplexer, each of the multiplexers having a control signal input coupled to a corresponding output of the controller, the controller selecting a particular one of the test data signals by application of a first control signal to the control signal input of the first multiplexer, and selecting the delayed version of the selected test data signal by application of a second control signal to the control signal input of the second multiplexer.
10. The data capture circuit of claim 1 wherein the controller circuit comprises a finite state machine (FSM).
11. The data capture circuit of claim 1 wherein the comparison circuit comprises (i) a logic gate having a first input adapted to receive the output signal generated by the first data capture device and a second input adapted to receive the output signal generated by the second data capture device, and (ii) a third data capture element having a data input coupled to an output of the logic gate, the third data capture element clocking data on a falling edge of the clock signal.
12. The data capture circuit of claim 1 wherein the circuit operates in a first mode in which the self-test capability is activated for application of the selected test data signal and the delayed version thereof to the respective first and second data capture elements, and a second mode in which the self-test capability is deactivated and a data signal is captured by at least one of the first and the second data capture elements.
13. An integrated circuit comprising:
at least one data capture circuit having a self-test capability, the data capture circuit comprising:
at least first and second data capture elements;
a controller for controllably selecting at least a particular one of a plurality of selectable clock-based test data signals for application to a data input of the first data capture element, a delayed version of the selected test data signal being applied to a data input of the second data capture element; and
a comparison circuit coupled between data outputs of the first and second data capture circuits and an input of the controller, the comparison circuit being configured to compare output signals generated by the first and second data capture elements, a result of the comparison being applied to the controller input;
wherein the controller repeats the controllable selection of particular test data signals and monitors corresponding comparison results until a clocking characteristic of at least one of the first and second data capture elements is determined to a desired level of accuracy.
14. The integrated circuit of claim 13 further comprising a clock generator circuit configured to generate (i) a clock signal for application to a clock input of the first and second data capture elements, and (ii) the plurality of selectable clock-based test data signals.
15. A method of providing a self-test capability in a data capture circuit including at least first and second data capture elements, the method comprising the steps of:
controllably selecting at least a particular one of a plurality of selectable clock-based test data signals for application to a data input of the first data capture element, a delayed version of the selected test data signal being applied to a data input of the second data capture element; and
comparing output signals generated by the first and second data capture elements;
wherein the selecting and comparing steps are repeated, with selection of one or more other ones of the selectable clock-based test data signals, until results of the comparing step until indicate that a clocking characteristic of at least one of the first and second data capture elements is determined to a desired level of accuracy.