Low-power voltage detector for low-voltage CMOS processes

Patent metadata

Field	Value
Publication number	US-11650656-B1
Application number	US-202217724635-A
Country	US
Kind code	B1
Filing date	Apr 20, 2022
Priority date	Apr 20, 2022
Publication date	May 16, 2023
Grant date	May 16, 2023

Abstract

A voltage detector has a diode ladder with one or more diodes connected in series between a battery voltage input and an upper measuring node. A measuring diode is connected between the upper measuring node and a lower measuring node. A resistor and a power-down switch are connected in series between the lower measuring node and a ground. An analog input to an Analog-to-Digital Converter (ADC) is connected by a switch to the upper measuring node to generate an upper digital value. Then the switch connects the analog input to the lower measuring node to generate a lower digital value. The difference between the upper and lower digital values is the diode voltage drop across the measuring diode and is multiplied by a number of diodes in the diode ladder and added to the upper digital value to generate a battery voltage measurement.

First claim

We claim:

1. A voltage detector comprising:
a diode ladder having one or more diodes connected in series between a voltage input and an upper measuring node;
a measuring diode connected between the upper measuring node and a lower measuring node;
a resistor and a power-down switch connected in series between the lower measuring node and a ground;
an Analog-to-Digital Converter (ADC) having an analog input and a digital output having a digital value that represents a voltage of the analog input;
a first switch that connects the upper measuring node to the ADC, the ADC generating an upper digital value representing a voltage of the upper measuring node;
a second switch that connects the lower measuring node to the ADC, the ADC generating a lower digital value representing a voltage of the lower measuring node; and
a controller that generates a calculated voltage measurement by generating a difference of the upper digital value and the lower digital value, and multiplying the difference by a number of diodes in the diode ladder to generate a product, and adding the product to the upper digital value to generate the calculated voltage measurement,
whereby a voltage across the measuring diode is measured and used to calculate the calculated voltage measurement.

2. The voltage detector of claim 1 wherein the diode ladder comprises an upper diode and a lower diode in series;
wherein the controller multiplies the difference by two to generate the product.

3. The voltage detector of claim 1 wherein the diode ladder comprises an upper diode and a middle diode and a lower diode in series;
wherein the controller multiplies the difference by three to generate the product.

4. The voltage detector of claim 3 wherein the one or more diodes in the diode ladder and the measuring diode each comprise a pn junction diode, wherein the one or more diodes in the diode ladder and the measuring diode are formed together in a semiconductor substrate.

5. The voltage detector of claim 4 wherein the one or more diodes in the diode ladder and the measuring diode are matched during design to have a same size and geometry.

6. The voltage detector of claim 5 wherein the one or more diodes in the diode ladder and the measuring diode are forward biased by the voltage input and the ground.

7. A voltage-measuring circuit comprising:
a voltage input;
a plurality of N diodes, wherein N is a whole number of diodes connected in series between the voltage input and a first node;
a measuring diode connected between the first node and a second node;
a resistor connected between the second node and a third node;
a power-down switch connected between the third node and a ground, the power-down switch opening to power down the voltage-measuring circuit when no voltage measurement is being made;
an Analog-to-Digital Converter (ADC) that converts a voltage of an analog input node to a digital value representing the voltage of the analog input node;
a first switch for connecting the first node to a combining node when the ADC generates the digital value as a first digital value representing a voltage of the first node;
a second switch for connecting the second node to the combining node when the ADC generates the digital value as a second digital value representing a voltage of the second node; and
a processor that receives the first digital value and the second digital value from the ADC and generates a digital estimate of a voltage of the voltage input, the processor subtracting the second digital value from the first digital value to generate a digital difference, multiplying the digital difference by N to generate a product, and adding the first digital value to the product to generate the digital estimate of the voltage of the voltage input,
whereby a voltage difference across the measuring diode is multiplied by a number of diodes in the plurality of N diodes and added to the first digital value to generate the digital estimate of the voltage of the voltage input.

8. The voltage-measuring circuit of claim 7 wherein the combining node is directly connected to the analog input node of the ADC.

9. The voltage-measuring circuit of claim 7 further comprising:
an analog buffer having the combining node as an input and the analog input node of the ADC as an output of the analog buffer.

10. The voltage-measuring circuit of claim 7 wherein each diode in the plurality of N diodes and the measuring diode each comprise a pn junction diode formed in a semiconductor substrate with other diodes in the plurality of N diodes.

11. The voltage-measuring circuit of claim 10 wherein the plurality of N diodes and the measuring diode are each forward biased by the voltage input and each has a diode voltage drop having a same value within 5%.

12. The voltage-measuring circuit of claim 7 wherein the ADC has at least 5 bits of precision, wherein the digital value generated by the ADC comprises at least 5 binary bits.

13. The voltage-measuring circuit of claim 7 wherein the measuring diode and each diode in the plurality of N diodes each comprise a diode-connected transistor having a gate and a drain connected together;
wherein the measuring diode and each diode in the plurality of N diodes are formed together in a semiconductor substrate.

14. The voltage-measuring circuit of claim 7 further comprising:
a third switch that connects a fixed voltage node to the ADC, the fixed voltage node having a fixed voltage.

15. The voltage-measuring circuit of claim 7 further comprising:
an amplifier having an input connected to the combining node, the amplifier having an output connected to the analog input node to the ADC.

16. The voltage-measuring circuit of claim 15 wherein the amplifier is an op amp, the op amp also having an inverting input that is connected to the output of the amplifier.

17. The voltage-measuring circuit of claim 7 wherein the first switch comprises a first n-channel transistor having a channel connected between the first node and the combining node, and having a control gate for isolating the first node from the combining node;
wherein the second switch comprises a second n-channel transistor having a channel connected between the second node and the combining node, and having a control gate for isolating the second node from the combining node.

18. The voltage-measuring circuit of claim 7 further comprising:
a battery connected to the voltage input;
wherein the power-down switch is opened to power down the voltage-measuring circuit to save battery power.

19. The voltage-measuring circuit of claim 18 wherein the power-down switch comprises an n-channel transistor having a channel connected in series with the resistor and having a control gate receiving a power-mode signal that causes the n-channel transistor to not conduct current from the resistor when the power-mode signal indicates a power-down mode.

20. A voltage measuring and protecting device comprising:
an Analog-to-Digital Converter (ADC) that converts an analog input node to a digital value representing a voltage of the analog input node;
wherein the digital value has at least 5 binary bits;
a voltage input for receiving an input voltage that is damaging to the ADC if directly applied to the analog input node;
a series of N diodes connected in series between the input voltage and a first node, each diode in the series of N diodes being forward biased by current from the voltage input, wherein N is a whole number;
a measuring diode connected between the firs

Assignees

• Hong Kong Applied Science & Tech Research Inst Co Ltd

Inventors

• Wong Wai Po
• Guo Huimin
• Lai Yat Tung

Classifications

• G05F3/247 Primary

  producing a voltage or current as a predetermined function of the supply voltage · CPC title

• G05F3/18

  using Zener diodes · CPC title

• G05F3/10

  using uncontrolled devices with non-linear characteristics · CPC title

• G05F1/571

  with overvoltage detector · CPC title

• G01R31/2632

  for testing diodes · CPC title