US 8,913,362 B2Granted

Diode protection of cascoded mixed-voltage transistors

AssigneeViXS Systems, Inc.

InventorDavid Simmonds

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Abstract

A mixed-voltage circuit employs a higher-voltage transistor in series connection with a lower-voltage transistor. To protect the lower-voltage transistor from transient overvoltage events, a series of one or more diodes is connected between the current terminals (i.e., the source and drain terminals) of the lower-voltage transistor so as to limit the voltage across the lower-voltage transistor. This diode protection mechanism also may be provided between the gate terminal and a current terminal of the lower-voltage transistor so as to protect against an overvoltage event at the gate of the lower-voltage transistor. In this manner, the mixed-voltage circuit can provide the performance benefits of mixed use of lower-voltage and higher-voltage transistors while reducing the risk of damaging the lower-voltage transistors due to the use of the higher-voltage power supply needed for operation of the mixed-voltage circuit.

Claims13

Dependent claims

A circuit comprising:

a first transistor comprising a first current terminal, a second current terminal, and a gate terminal, the first transistor having a first operational voltage level and the first current terminal coupled to an output terminal to provide an output signal;
a second transistor comprising a first current terminal, a second current terminal, and a gate terminal, the first current terminal of the second transistor coupled to the second current terminal of the first transistor, the second transistor having a second operational voltage level lower than the first operational voltage level and the gate terminal coupled to an input terminal to receive an input signal;
a first series of one or more diodes connected in series between the first current terminal and the second current terminal of the second transistor, a first diode of the first series having an anode terminal coupled to the first current terminal of the second transistor and a last diode of the first series having a cathode terminal coupled to the second current terminal of the second transistor;
a second series of one or more diodes connected between the gate terminal of the second transistor and the second current terminal of the second transistor, a first diode of the second series having an anode terminal coupled to the gate terminal of the second transistor and a last diode of the second series having a cathode terminal coupled to the second current terminal of the second transistor;
and
a third series of one or more diodes connected between the gate terminal of the second transistor and the second current terminal of the second transistor, a first diode of the third series having an anode terminal coupled to second current terminal of the second transistor and a last diode of the third series having a cathode terminal coupled to the gate terminal of the second transistor.

3 more elements

A method comprising:

providing a circuit comprising a first transistor comprising a first current terminal coupled to an output terminal for providing an output signal, a second current terminal, and a gate terminal, the first transistor having a first operational voltage level, a second transistor comprising a first current terminal, a second current terminal, and a gate terminal coupled to an input terminal to receive an input signal, the first current terminal of the second transistor coupled to the second current terminal of the first transistor, and the second transistor having a second operational voltage level lower than the first operational voltage level, and a first series of one or more diodes connected in series between the first current terminal and the second current terminal of the second transistor, a first diode of the first series having an anode terminal coupled to the first current terminal of the second transistor and a last diode of the first series having a cathode terminal coupled to the second current terminal of the second transistor, the circuit further comprising a second series of one or more diodes connected between the gate terminal of the second transistor and the second current terminal of the second transistor, a first diode of the second series having an anode terminal coupled to the gate terminal of the second transistor and a last diode of the second series having a cathode terminal coupled to the second current terminal of the second transistor;
and the circuit further comprising a third series of one or more diodes connected between the gate terminal of the second transistor and the second current terminal of the second transistor, a first diode of the third series having an anode terminal coupled to second current terminal of the second transistor and a last diode of the third series having a cathode terminal coupled to the gate terminal of the second transistor;
and
operating the circuit at a first time such that a voltage difference between the first current terminal and the second current terminal of the second transistor is not greater than the second voltage level.

1 more element

Dependencies are inferred from the claim text.