Protection circuits for tunable resistor at continuous-time ADC input
AssigneeAnalog Devices Global
InventorHajime Shibata
Life of this patent
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Abstract
Continuous-time analog-to-digital converters (ADCs) such as continuous-time delta-sigma ADCs and continuous-time pipeline ADCs, has input resistor structure at the input. The input resistor structure is typically tunable, and the tunability is usually provided by metal-oxide semiconductor field effect transistor (MOSFET) switches. Core MOSFETs, which has a terminal-to-terminal voltage <1.0V, is used for the switches for performance reasons. However, a typical implementation can have reliability issues with overloading inputs. An improved input resistor protection circuit can solve this issue by generating on and off voltages for the switches inside the tunable resistor structure based on a summing node voltage where one side of the switch is connected.
Claims20
A method for protecting a tunable resistor circuit at an input of an analog-to-digital converter (ADC), the method comprising:
- generating a first voltage and a second voltage based on a voltage at a summing node of an operational amplifier of the ADC;
- and
- driving a transistor coupled to a resistor slice of the tunable resistor circuit with the first voltage to switch in the resistor slice;
- wherein the transistor is coupled to the summing node and the resistor slice is coupled to an input terminal of the ADC and the transistor.
A tunable resistor circuit at an input of an analog-to-digital converter (ADC), the tunable resistor comprising:
- resistor slices in parallel, wherein each resistor slice is coupled to an input terminal of the ADC;
- transistors coupled to respective resistor slices and a summing node of an operational amplifier of the ADC for switching the resistor slices in and out of the tunable resistor circuit;
- and
- drivers coupled to respective transistors for generating on and off voltages for the transistors from a voltage at the summing node.
An apparatus comprising:
- a tunable resistor circuit having parallel resistor slices and corresponding switches, said tunable resistor circuit being coupled to an input of an ADC and a summing node of an operational amplifier of the ADC;
- and
- means for generating voltages for controlling on and off states of the switches, wherein the voltages follow a voltage of the summing node.
Dependencies are inferred from the claim text.