Clamped push-pull driver circuit with output feedback

摘要

A clamped push-pull driver circuit suitable for driving high capacitive loads includes a bootstrap MOS inverter circuit driving an MOS push-pull driver circuit. A regulator circuit including a plurality of diode-connected MOSFETs is coupled between the output of the MOS bootstrap inverter and a ground conductor. A MOSFET (the feedback device) having its gate electrode coupled to the output of the MOS push-pull circuit is connected in series with the diode-connected MOSFETs. Rapid rise time and short delay are achieved at the output of the clamped push-pull driver circuit, since the regulator circuit does not begin to conduct current (i.e., does not start the clamping action) until the output voltage of the push-pull driver circuit has exceeded two thresholds. Thus a large drive capability is provided to initiate the rising action of the output signal and clamping only begins to occur after the output is already rising towards a higher virtual final level than that which clamping will allow. This delayed clamping action is controlled by the feedback MOSFET which is positioned between two of the diode-connected MOSFETs so that the feedback MOSFET is not turned on until the desired voltage is achieved at the output of the MOS push-pull driver circuit. The output of the MOS push-pull driver will continue to rise until it reaches a level which is one threshold below that set by the plurality of diode-connected MOSFETs. The final voltage, at the end of the rise time, at the output of the MOS push-pull driver circuit tracks with the MOS threshold voltage.