Fault tolerant asynchronous circuits
New and improved methods and circuit designs for asynchronous circuits that are tolerant to transient faults, for example of the type introduced through radiation or, more broadly, single-event effects. SEE-tolerant configurations are shown and described for combinational logic circuits, state-holding logic circuits and SRAM memory circuits.
1. A fault tolerant asynchronous circuit, comprising:
a first circuit node;
a second circuit node;
a plurality of C elements comprising a first plurality of directly and serially connected pass transistors connecting the first circuit node and the second circuit node, each of the first plurality of directly and serially connected pass transistors being controlled by a replica of a gating signal that is not the same signal as the gating signal, the gating signal being connected to a second plurality of directly and serially connected pass transistors; and
a plurality of weak-C elements corresponding in number to the plurality of C elements, an output of at least one of the plurality of weak-C elements being directly coupled to each of the plurality of C elements.
2. The circuit of claim 1 , wherein the first plurality of directly and serially connected pass transistors comprises at least one N-type transmission gate or at least one P-type transmission gate.
3. The circuit of claim 1 , wherein
the plurality of C elements are configured to be operated by a plurality of gating signals and their replicas, including the gating signal and the replica of the gating signal.
4. The circuit of claim 1 , further comprising:
inverters to directly couple the C elements to the weak-C elements.
5. The circuit of claim 1 , further comprising:
inverters in a direct feedback path from the weak-C elements to the C elements.
6. The circuit of claim 1 , further comprising:
a first double transistor gate to provide the gating signal; and
a second double transistor gate to provide the replica of the gating signal.
7. The circuit of claim 1 , wherein the first plurality of directly and serially connected pass transistors form part of a static random access memory circuit.
8. The circuit of claim 1 , further comprising:
at least four cross-coupled C elements comprising the first plurality of directly and serially connected pass transistors.
9. The circuit of claim 1 , further comprising:
at least one read line coupled to the first and second circuit nodes.
10. The circuit of claim 1 , wherein each of the plurality of weak-C elements is directly coupled to each of the plurality of C elements.