Signal switch with reduced on resistance and undershoot protection
AssigneeTexas Instruments Incorporated
InventorChristopher M. Graves
Life of this patent
Estimating the term…
Abstract
An electronic switch applies ground potential to the backgate of a MOS pass transistor when the transistor is in the off state and the switch is open, during normal conditions. When the transistor is switched to the on state and the switch is closed, the gate voltage is applied to the backgate of the pass transistor in order to reduce the threshold voltage and the on resistance. During an undershoot condition, the gate of the pass transistor is connected to the negative voltage applied to an input port and this voltage is also connected to the backgate of the pass transistor to prevent the pass transistor from being biased on or the parasitic NPN transistor from being biased on and transmitting the input glitch to the output.
Claims20
A signal switch comprising:
- an MOS pass transistor coupled between a first port and a second port;
- a drive circuit coupled to a gate and a back gate of the MOS pass transistor
- an undershoot detection circuit coupled to the path between ports for detecting an undershoot condition;
- and
- an undershoot protection circuit coupled to an output of the undershoot detection circuit and to the gate and back gate of the MOS pass transistor for preventing the MOS pass transistor from being turned on by the undershoot and creating a bus disturbance.
In a signal switch having a MOS pass transistor coupled between a signal input and a signal output, a driver circuit comprising:
- a first biasing circuit coupled to a back gate of the MOS pass transistor for reducing the VT of the MOS pass transistor when the MOS pass transistor is turned ON to allow a signal at the signal input to propagate to the signal output;
- and
- a second biasing circuit coupled to a gate and the back gate of the MOS pass transistor to prevent an undershoot from propagating to the signal output.
Dependencies are inferred from the claim text.