  We present two designs for an analog circuit that can learn to detect a
temporal sequence of two inputs. The training phase is done by feeding the
circuit with the desired sequence and, after the training is completed, each
time the trained sequence is encountered again the circuit will emit a signal
of correct recognition. Sequences are in the order of tens of nanoseconds. The
first design can reset the trained sequence on runtime but assumes very strict
timing of the inputs. The second design can only be trained once but is lenient
in the input's timing.
