High Speed Wide Dynamic Range Input Structure

A method for protecting a circuit input from input voltage fluctuations at a voltage input, comprising:

• connecting the voltage input to the circuit input over a signal path in a protection circuit comprising a first cascode switch, a level shifter, and a second cascode switch connected in series between the voltage input and circuit input;
• and
• generating, by the protection circuit, an output voltage at the circuit input that is a threshold voltage below the input voltage when the input voltage at the voltage input is within a specified voltage range for linear operation of the protection circuit;
• wherein the first cascode switch is connected between a first current source and a blocking field effect transistor connected to a power supply voltage to provide negative voltage excursion protection at the circuit input when the input voltage at the voltage input is below a specified voltage range for linear operation of the protection circuit,
• wherein the second cascode switch is connected between a second current source and the power supply voltage to provide positive voltage excursion protection at the circuit input when the input voltage at the voltage input is above the specified voltage range for linear operation of the protection circuit, and
• wherein the level shifter is connected between a third current source and a resistor circuit connected to the power supply voltage to operate as a source follower with a threshold voltage drop VTH.

An input protection circuit for generating an output voltage from an input voltage received at a voltage input, comprising:

• a first cascode switch connected between a first current source and a blocking field effect transistor connected to a power supply voltage, where the first cascode switch provides negative voltage excursion protection at the output voltage when the input voltage is below a specified voltage range for linear operation of the input protection circuit, where the first cascode switch comprises a high-voltage FET of a first polarity type having a control electrode, a first current carrying electrode connected across a first zener diode to the control electrode, and a second current carrying electrode connected to receive the input voltage;
• a second cascode switch connected between a second current source and the power supply voltage, where the second cascode switch provides positive voltage excursion protection at the output voltage when the input voltage is above a specified voltage range for linear operation of the input protection circuit, where the second cascode switch comprises a high-voltage FET of a second polarity type having a control electrode connected to the power supply voltage, a first current carrying electrode providing the output voltage and connected across a second zener diode to the control electrode, and a second current carrying electrode connected to a source follower node;
• a blocking field effect transistor (FET) of the second polarity type connected between a third current source and the power supply voltage to provide reverse protection gate bias to the high-voltage FET of the first polarity type, where the blocking FET comprises a control electrode connected to a power supply voltage, a first current carrying electrode connected across a third zener diode to the power supply voltage, and a second current carrying electrode connected to the control electrode of the high-voltage FET of the first polarity type;
• and
• a level shifter circuit connected between a fourth current source and a resistor circuit connected to the power supply voltage, where the level shifter circuit operates as a source follower between the first current carrying electrode of the high-voltage FET of the first polarity type and the source follower node.