Comparator for input voltages higher than supply voltage
First Claim
1. A comparator for comparing voltages of first and second inputs, comprising:
- first and second current paths coupled to the first and second inputs respectively, the first current path passing from the first input through a first main electrode and a second main electrode of a first transistor, and through a first bias current source to a supply line;
the second current path passing through a reference voltage drop element, through a first main electrode and a second main electrode of a second transistor, and through a second bias current source to said supply line, the comparator further comprising a diode coupled to the first input to protect the first input from current flow through forward biasing of a parasitic diode from said second main electrode to a bulk of the first transistor.
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Abstract
A comparator has first and second current paths, each passing from an input through a transistor, through a current source to ground, the second current path also having a reference voltage drop element coupled in series with the second input. The gates of the transistors are coupled to form a current mirror. The reference voltage drop element enables higher voltages to be input and compared to higher thresholds above an internal supply voltage level without the need for dividing resistors to reduce the input voltage. Avoiding such resistors means the power dissipation and the silicon area used can be kept lower. ESD vulnerability is reduced since the inputs are not coupled to gates of MOS transistors. Overvoltage protection across the source and gate of the second transistor can be added.
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Citations
11 Claims
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1. A comparator for comparing voltages of first and second inputs, comprising:
- first and second current paths coupled to the first and second inputs respectively, the first current path passing from the first input through a first main electrode and a second main electrode of a first transistor, and through a first bias current source to a supply line;
the second current path passing through a reference voltage drop element, through a first main electrode and a second main electrode of a second transistor, and through a second bias current source to said supply line, the comparator further comprising a diode coupled to the first input to protect the first input from current flow through forward biasing of a parasitic diode from said second main electrode to a bulk of the first transistor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
- first and second current paths coupled to the first and second inputs respectively, the first current path passing from the first input through a first main electrode and a second main electrode of a first transistor, and through a first bias current source to a supply line;
Specification