Microcontroller with average current measurement circuit using voltage-to-current converters

Patent metadata

Field	Value
Publication number	US-10044264-B2
Application number	US-201615157879-A
Country	US
Kind code	B2
Filing date	May 18, 2016
Priority date	May 20, 2015
Publication date	Aug 7, 2018
Grant date	Aug 7, 2018

Abstract

The average of a complex waveform measured over a time period may be determined by first converting the complex waveform to a voltage, then converting this voltage to a current and using this current to charge a capacitor. At the end of the measurement time period the voltage charge (sample voltage) on the capacitor may be sampled by a sample and hold circuit associated with an analog-to-digital converter (ADC). Then the voltage charge on the sample capacitor may be removed, e.g., capacitor plates shorted by a dump switch in preparation for the next average of the complex waveform sample measurement cycle. The ADC then converts this sampled voltage charge to a digital representation thereof and a true average of the complex waveform may be determined, e.g., calculated therefrom in combination with the measurement time period.

First claim

The invention claimed is:

1. A microcontroller, comprising:
an external connection configured to receive a voltage from a shunt resistor;
a voltage-to-current converter having an input coupled to the external connection and adapted to convert the voltage to a current, wherein an output of the voltage-to-current converter is coupled to a sample capacitor and the current therefrom charges the sample capacitor to a sample voltage during a measurement time period;
at least one sample time period adjustment capacitor configured to be selectively switched in parallel with the sample capacitor;
an analog-to-digital converter (ADC) configured to be coupled to the sample capacitor after the measurement time period is over, wherein the ADC samples and then converts the sample voltage on the sample capacitor to a digital representation thereof; and
a sample voltage reset switch coupled to the sample capacitor, wherein the sample voltage reset switch resets the sample capacitor to a substantially zero voltage after the ADC has sampled the sample voltage thereon.

2. The microcontroller according to claim 1 , further comprising a programmable gain amplifier (PGA) coupled between the external connection and the input of the voltage-to-current converter.

3. The microcontroller according to claim 2 , further comprising a level shifter coupled between the PGA and the voltage-to-current converter.

4. The microcontroller according to claim 1 , wherein the sample capacitor is also used as a sample and hold capacitor for the ADC.

5. The microcontroller according to claim 1 , further comprising a buffer amplifier coupled between the sample capacitor and the ADC.

6. The microcontroller according to claim 5 , wherein the buffer amplifier has differential outputs and differential inputs, wherein the differential inputs thereof are coupled to the sample capacitor differentially.

7. The microcontroller according to claim 1 , wherein the voltage-to-current converter is an operational transconductance amplifier (OTA).

8. The microcontroller according to claim 7 , wherein the OTA comprises differential outputs coupled to the sample capacitor differentially.

9. The microcontroller according to claim 7 , further comprising a programmable gain amplifier (PGA) having differential outputs and differential inputs, wherein the PGA is coupled between first and second external connections and differential inputs of the OTA.

10. The microcontroller according to claim 1 , further comprising an average current measurement controller coupled to a sample capacitor switch, at least one sample period adjustment capacitor switch, and the sample voltage reset switch.

11. A switch mode power supply (SMPS), comprising:
a power inductor having a first end coupled to a power source;
a power switch coupled to a second end of the power inductor;
a current measurement resistor coupled to the power switch and in series with power inductor, wherein a voltage across the current measurement resistor is proportional to current through the power inductor;
a rectifier coupled to the second end of the power inductor and the power switch;
a filter capacitor coupled to the rectifier;
a microcontroller, comprising:
a connection configured to receive the voltage from the current measurement resistor;
a voltage-to-current converter having an input coupled to the connection and adapted to convert the voltage to a current, wherein an output of the voltage-to-current converter is coupled to a sample capacitor and the current therefrom charges the sample capacitor to a sample voltage during a measurement period;
an analog-to-digital converter (ADC) configured to be coupled to the sample capacitor after the measurement period is over, wherein the ADC samples and then converts the sample voltage on the sample capacitor to a digital representation thereof;
a sample voltage reset switch coupled to the sample capacitor, wherein the sample voltage reset switch resets the sample capacitor to a substantially zero voltage after the ADC has sampled the sample voltage thereon;
a SMPS controller coupled to the ADC and the power switch, and using the digital representation of the sample voltage when controlling the power switch; and
a digital processor and memory.

12. A method for determining an average of a complex voltage waveform, said method comprising the steps of:
generating an external voltage by a shunt resistor; and
within a microcontroller performing the steps of:
coupling the external voltage to a voltage-to-current converter;
converting the external voltage to a current with the voltage-to-current converter;
coupling the current to a sample capacitor for a measurement time period, wherein the current charges the sample capacitor to a sample voltage during the measurement time period, wherein the step of coupling the current to a sample capacitor further comprises the step of: switching in parallel with the sample capacitor at least one sample time period adjustment capacitor for increasing a useable measurement time period;
sampling the sample voltage after the measurement time period with an analog-to-digital converter (ADC);
converting the sampled sample voltage to a digital representation thereof with the ADC;
resetting the sample capacitor to a substantially zero voltage after the ADC has sampled the sample voltage thereon; and
determining an average of the external voltage taken over the measurement time period from the digital representation of the sampled sample voltage.

13. The method according to claim 12 , further comprising the step of controlling gain of a programmable gain amplifier (PGA) coupled between the external voltage and the voltage-to-current converter.

14. The method according to claim 12 , wherein the voltage-to-current converter is an operational transconductance amplifier (OTA).

15. The method according to claim 12 , wherein the step of sampling the sample voltage is done with a sample and hold circuit associated with the ADC.

16. A microcontroller, comprising:
an external connection configured to receive a voltage;
a voltage-to-current converter having an input coupled to the external connection and adapted to convert the voltage to a current, wherein an output of the voltage-to-current converter is coupled to a sample capacitor and the current therefrom charges the sample capacitor to a sample voltage during a measurement time period;
at least one sample time period adjustment capacitor configured to be selectively switched in parallel with the sample capacitor;
an analog-to-digital converter (ADC) configured to be coupled to the sample capacitor after the measurement time period is over, wherein the ADC samples and then converts the sample voltage on the sample capacitor to a digital representation thereof; and
a sample voltage reset switch coupled to the sample capacitor, wherein the sample voltage reset switch resets the sample capacitor to a substantially zero voltage after the ADC has sampled the sample voltage thereon.

17. The microcontroller according to claim 16 , further comprising a programmable gain amplifier (PGA) coupled between the external connection and the input of the voltage-to-current converter.

18. The microcontroller according to claim 17 , further comprising a level shifter coupled between the PGA and the voltage-to-current converter.

19. The microcontroller according to claim 16 , wherein the sample capacitor is also used as a sample and hold capacitor for the ADC.

20. The microcontroller according to

Assignees

• Microchip Tech Inc

Inventors

• Kris Bryan
• Bartling James

Classifications

• H02M3/156 Primary

  with automatic control of output voltage or current, e.g. switching regulators · CPC title

• H03G3/20

  Automatic control ({H03G3/005 takes precedence;} combined with volume compression or expansion H03G7/00) · CPC title

• H02M1/08

  Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters · CPC title

• G01R19/003 Primary

  Measuring mean values of current or voltage during a given time interval · CPC title

• G01R19/255

  using analogue/digital converters of the type with counting of pulses during a period of time proportional to voltage or current, delivered by a pulse generator with fixed frequency · CPC title