High voltage detection circuit

• US 4,659,944 A
• Filed: 04/08/1985
• Issued: 04/21/1987
• Est. Priority Date: 04/08/1985
• Status: Expired due to Fees

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Ulmer, Richard W., Miller, James A. Sr., Allgood, Robert N.
• Primary Examiner(s): Zazworsky, John
• Application Number:
  US06/720,789
• Time in Patent Office: 743 Days
• Field of Search: 307/350, 307/354, 307/362, 307/363, 307/296 R
• US Class Current: 327/97
• CPC Class Codes: H03K 17/302 in field-effect transistor switches
• CPC Class Codes: H03K 17/6872 using complementary field-effect transistors

Abstract

A voltage detecting circuit is provided for generating an output signal when an input signal exceeds the power supply voltage by a predetermined amount. A reference current is established by an output stage using a first current mirror. A second current mirror is connected to the output stage and detects the input voltage level by forcing a greater or lesser amount of current through the output stage to provide a high or low level output voltage.

Claims

1. A circuit for providing an output signal having a voltage level of a predetermined magnitiude in response to an input voltage having an absolute magnitude greater than an absolute magnitude of an reference voltage, comprising:

a current source for providing a reference current;

first means coupled to the current source for providing a first control voltage;

second means, having a terminal adapted to receive the input voltage and providing a second control voltage in response to the magnitude of the input voltage relative to the reference voltage; and

an output stage coupled to the first and second means, for providing the output signal in response to the first and second control voltages, said first control voltage establishing a sink current of the output stage proportional to the reference current, and said second control voltage establishing a first predetermined source current if the input voltage magnitude is greater than the reference voltage magnitude and establishing a second predetermined source current otherwise.

2. The circuit of claim 1 wherein the first means for providing the first control voltage to establish the sink current of the output stage is a current mirror.

3. The circuit of claim 1 wherein the output stage comprises;

a first transistior of a first conductivity type having a first electrode coupled to a first reference voltage terminal, a control electrode for receiving the second control voltage, and a second current electrode for providing the output signal; and

a second transistior of a second conductivity type having a first electrode coupled to the second electrode of the first transistor, a control electrode for receiving the first control voltage, and a second current electrode coupled to a second

4. The circuit of claim 1 wherein the second means further comprise:

a first transistor of a first conductivity type having a first current electrode connected to a terminal for receiving the reference voltage, a control electrode for receiving the input voltage, and a second current electrode;

a second transistor of a second conductivity type having a first current electrode connected to the second current electrode of the first transistor, and both a control electrode and a second current electrode connected together; and

a third transistor of the second conductivity type having a first current electrode connected to the terminal for receiving the reference voltage, and both a control electrode and a second current electrode connected to the control electrode and the second current electrode of the second transistor, for providing the second control voltage.

5. A method for producing an output voltage of a predetermined magnitude in response to an input signal having an absolute magnitude greater than an absolute magnitude of a reference voltage, comprising the steps of:

providing an output stage for providing the output voltage;

providing a current source for providing a reference current;

providing a first control voltage in response to the reference current;

coupling the first control voltage to the output stage to establish a predetermined sink current of the output stage proportional to the reference current;

providing a second control voltage having a magnitude proportional to the voltage magnitude of the input signal relative to the reference voltage; and

coupling the second control voltage to the output stage to establish a first predetermined source current in the output stage if the input voltage magnitude is greater than the reference voltage magnitude and otherwise establishing a second predetermined source current in the output stage.

6. A circuit for producing a predetermined output signal of a first magnitude in response to an input voltage having an absolute value greater than an absolute value of a predetermined supply voltage, comprising:

a current source for providing a reference current of a second magnitude;

an output node formed by serially connecting current conducting electrodes of a first transistor and a second transistor, each of which is a current mirroring transistor;

the first transistor sinking a first predetermined current from the output node having a first current magnitude proportional to the reference current;

a current mirror connected to the second transistor, said second transistor providing a source current to the output node which maintains either a second current magnitude when the absolute value of the input signal is any value above the absolute value of the predetermined supply voltage or which maintains a third current magnitude when the absolute value of the input signal is any value equal to or less than the absolute value of the predetermined supply voltage.