| 摘要 |
<p>An improved output circuit (109") for an operational amplifier which is controlled to operate in one or two modes. In the first mode, the output of the operational amplifier tracks a reference signal or ground. In the second mode, the output of the operational amplifier tracks the level of a time varying second voltage signal. The improvement consists of replacing the stabilization capacitor of prior art output circuits (109) with a pair of stabilization capacitors (123 and 125) connected in parallel. Each of the pair of capacitors has an associated series connected switch (127 and 129) for switching the capacitor into and out of the circuit. The switches are operated by a respective one of a pair of external non-overlapping clock pulse trains (PHI1 and phi2) so as not to be closed simultaneously. The effect of this improved output circuit (109") is to allow the output voltage of the operational amplifier to slew rapidly (or snap) up to the last previous level of a sampled input voltage (or a predetermined second reference voltage) thereby minimizing the effects imposed by the limiting of the first stage slew rate. Thus, slewing begins at a higher rate, governed primarily by the higher slew rate capability of the output stage, and consumes less time. In addition, the output voltage will snap directly from the level of the sampled time varying second voltage to the reference voltage level at the same high slew rate of the output stage. Because the voltage difference through which the stabilization capacitor must charge is greatly reduced, the output is able to reach and track the time varying voltage more rapidly than can prior art devices. The output of the operational amplifier thus shows greater correlation with the level of the second or time varying signal. </p> |
