Resistor-programmable device at low voltage

• US 8,237,467 B2
• Filed: 06/25/2010
• Issued: 08/07/2012
• Est. Priority Date: 06/25/2010
• Status: Active Grant

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Lorenz, Perry Scott
• Primary Examiner(s): JAGER, RYAN C
• Application Number:
  US12/803,368
• Publication Number:
  US 20110316588A1
• Time in Patent Office: 774 Days
• Field of Search: 326/30, 326/82, 327/77
• US Class Current: 326/82
• CPC Class Codes: H03M 1/56 Input signal compared with linear ramp
• CPC Class Codes: H03M 11/24 using analogue means , e.g. by coding the states of multiple switches into a single multi-level analogue signal or by indicating the type of a device using the voltage level at a specific tap of a resistive divider

Abstract

A resistor-programmable device generates pulses counted by a counter. The counter'"'"'s output controls a drive signal generator, such as an adjustable current source. The drive signal generator generates a drive signal (such as a current), which leads to the creation of a sense signal (such as a voltage) using a resistance. The resistance can have one of a set of specified values or fall within one of a set of specified windows. The resistor-programmable device can convert the resistance value into a digital value, which can be used to set a sensor trip point threshold or some other parameter. The digital or parameter value is independent of changes in the resistance that are within a specified tolerance. For instance, the same parameter value could be selected even when the resistance varies within some tolerance (such as 1%) as the resistor-programmable device can determine the window in which the resistance falls.

Claims

1. A method comprising:

providing a drive signal to a specified one of multiple resistances via at least one switch, the drive signal based on a counter value that is output by a counter;

generating a sense signal based on the drive signal using the specified resistance;

determining if the sense signal passes a threshold;

if the sense signal does not pass the threshold, changing the counter value that is output by the counter and repeating the providing, generating, and determining steps; and

if the sense signal does pass the threshold, providing the counter value to a demultiplexer for storage in at least one register.

2. The method of claim 1, further comprising:

repeating the providing, generating, determining, and changing steps to identify a second counter value associated with a second specified one of the multiple resistances.

3. The method of claim 2, further comprising:

providing the second counter value to the demultiplexer for storage in the at least one register.

4. The method of claim 2, wherein the at least one register comprises a single multi-bit register.

5. The method of claim 1, further comprising:

identifying at least one parameter value of a resistor-programmable device based on the counter value;

wherein the at least one parameter value is independent of changes in the specified resistance that are within a specified tolerance.

6. The method of claim 1, wherein:

generating the drive signal comprises generating an adjustable current;

generating the sense signal comprises generating a voltage across the specified resistance; and

changing the counter value that is output by the counter comprises incrementing the counter value.

7. A method comprising:

providing a drive signal based on a counter value that is output by a counter;

generating a sense signal based on the drive signal using a resistance;

determining if the sense signal passes a threshold;

if the sense signal does not pass the threshold, changing the counter value that is output by the counter and repeating the providing, generating, and determining steps;

if the sense signal does pass the threshold, generating a trip point threshold based on the counter value; and

comparing an output signal from a sensor to the trip point threshold in order to determine whether the output signal is less than or greater than the trip point threshold.

8. An apparatus comprising:

a pulse generator configured to generate pulses in a pulse signal;

a counter configured to receive the pulse signal and to output a counter value that varies based on a number of received pulses;

a drive signal generator configured to generate a drive signal based on the counter value in order to generate a sense signal using a resistance, the sense signal based on the drive signal;

a comparator configured to determine if the sense signal passes a threshold, wherein the pulse generator is configured to generate the pulses in the pulse signal until the comparator outputs a signal indicating that the threshold is passed; and

a digital-to-analog converter configured to generate a trip point threshold for a sensor based on the counter value that is output by the counter when the comparator outputs the signal indicating that the threshold is passed.

9. The apparatus of claim 8, further comprising:

a register configured to store the counter value that is output by the counter when the comparator outputs the signal indicating that the threshold is passed;

wherein the digital-to-analog converter is configured to generate the trip point threshold for the sensor based on the counter value stored in the register.

10. The apparatus of claim 8, further comprising:

a reset unit configured to turn the pulse generator on in response to a triggering event.

11. The apparatus of claim 8, wherein:

the drive signal generator comprises at least one adjustable current source; and

the apparatus further comprises a voltage source configured to provide a voltage as the threshold to the comparator.

12. The apparatus of claim 8, wherein the counter is configured to increment the counter value in response to each pulse in the pulse signal.

13. The apparatus of claim 8, wherein:

the apparatus is configured to output a digital value based on multiple resistances;

each of the multiple resistances has a resistance that (i) equals one of multiple specified values or (ii) falls within one of multiple specified windows; and

the digital value is based on the specified value or specified window associated with each of the resistances.

14. An apparatus comprising:

a pulse generator configured to generate pulses in a pulse signal;

a counter configured to receive the pulse signal and to output a counter value that varies based on a number of received pulses;

a drive signal generator configured to generate a drive signal based on the counter value in order to generate a sense signal, the sense signal based on the drive signal;

a comparator configured to determine if the sense signal passes a threshold, wherein the pulse generator is configured to generate the pulses in the pulse signal until the comparator outputs a signal indicating that the threshold is passed;

a register configured to store the counter value that is output by the counter when the comparator outputs the signal indicating that the threshold is passed;

at least one switch configured to couple one of multiple resistances to the drive signal generator; and

a demultiplexer coupled between the counter and the register.

15. A system comprising:

a resistor-programmable device configured to output a digital value associated with a trip point of a sensor;

a digital-to-analog converter configured to convert the digital value into an analog trip point threshold; and

a first comparator configured to compare an output signal from the sensor to the analog trip point threshold;

wherein the resistor-programmable device comprises;

a pulse generator configured to generate pulses in a pulse signal;

a counter configured to receive the pulse signal and to output a counter value that varies based on a number of received pulses;

a drive signal generator configured to generate a drive signal based on the counter value in order to generate a sense signal using a resistance, the sense signal based on the drive signal; and

a second comparator configured to determine if the sense signal passes a threshold;

wherein the pulse generator is configured to generate the pulses in the pulse signal until the second comparator outputs a signal indicating that the threshold is passed, the digital value based on the counter value that is output by the counter when the comparator outputs the signal indicating that the threshold is passed.

16. The system of claim 15, wherein the resistor-programmable device further comprises:

a register configured to store the counter value that is output by the counter when the second comparator outputs the signal indicating that the threshold is passed;

wherein the digital-to-analog converter is configured to generate the analog trip point threshold for the sensor based on the counter value stored in the register.

17. The system of claim 16, wherein:

the system further comprises at least one switch configured to couple one of multiple resistances to the drive signal generator; and

the resistor-programmable device further comprises a demultiplexer coupled between the counter and the register.

18. The apparatus of claim 15, wherein the resistor-programmable device further comprises:

a reset unit configured to turn the pulse generator on in response to a triggering event.

19. The system of claim 15, wherein:

the drive signal generator comprises at least one adjustable current source; and

the resistor-programmable device further comprises a voltage source configured to provide a voltage as the threshold to the second comparator.

20. The system of claim 15, wherein:

the resistor-programmable device is configured to output the digital value based on multiple resistances;

each of the multiple resistances has a resistance that (i) equals one of multiple specified values or (ii) falls within one of multiple specified windows; and

the digital value is based on the specified value or specified window associated with each of the resistances.