A thermally compensated circuit includes a first adjustable circuit, like an adjustable current source, to produce a first adjustable signal, such a reference current. The circuit includes a second adjustable circuit to produce a second adjustable signal, such as a reference voltage. Circuitry responsive to the first and second adjustable signals produces an output, such as a clock signal. A tunable circuit in the first adjustable circuit and a tunable first element of the second adjustable circuit set an operating characteristic, such as a clock period, of the output to a target level at a first temperature. A tunable second element of the second adjustable circuit sets the operating characteristic of the output signal at the target level at a second temperature. Tuning of the second tunable element at the second temperature does not substantially change the operating characteristic of the output signal at the first temperature.