Current measurement

Patent metadata

Field	Value
Publication number	US-9638724-B2
Application number	US-201414290820-A
Country	US
Kind code	B2
Filing date	May 29, 2014
Priority date	Jun 1, 2013
Publication date	May 2, 2017
Grant date	May 2, 2017

Abstract

Current measurement apparatus comprises a measurement arrangement and a signal source. The measurement arrangement is configured to measure a current signal drawn by a load. The signal source is operative to apply a reference input signal to the measurement arrangement whereby an output signal from the measurement arrangement comprises a load output signal corresponding to the load drawn current signal and a reference output signal corresponding to the reference input signal. The signal source comprises a current multiplier which defines first and second current paths and is configured such that: the first path carries a multiplier input current signal; the second path carries a multiplier output current signal which determines the reference input signal and which corresponds to the multiplier input current signal multiplied by a multiplier value determined by the current multiplier; and the multiplier input current signal and the multiplier output current signal are carried on their respective paths in a same direction relative to a power supply voltage. Power drawn through the second path as divided by the multiplier value is less than the power drawn through the first path.

First claim

The invention claimed is:

1. Current measurement apparatus comprising:
a measurement arrangement configured to be disposed in relation to a load which draws a load drawn current signal, the measurement arrangement being operative when so disposed to measure the load drawn current signal;
a signal source operative to apply a reference input signal to the measurement arrangement whereby an output signal from the measurement arrangement comprises a load output signal corresponding to the load drawn current signal and a reference output signal corresponding to the reference input signal; and
processing apparatus which is operative to receive the output signal and to make a determination in dependence on the reference output signal, in which
the signal source comprises a current multiplier which defines first and second current paths, the current multiplier being configured such that: the first path carries a multiplier input current signal; the second path carries a multiplier output current signal which determines the reference input signal and which corresponds to the multiplier input current signal multiplied by a multiplier value determined by the current multiplier; and the multiplier input current signal and the multiplier output current signal are carried on their respective paths in a same direction relative to a power supply voltage, and
the signal source is configured such that power drawn through the second path as divided by the multiplier value is less than the power drawn through the first path.

2. Current measurement apparatus according to claim 1 in which the current multiplier is configured to increase a current level in the second path relative to the first path by more than one order of magnitude.

3. Current measurement apparatus according to claim 1 in which the signal source is configured such that the reference input signal is determined by the multiplier output current signal and the multiplier input current signal.

4. Current measurement apparatus according to claim 3 in which the current multiplier is configured such that the first and second paths combine whereby the multiplier output current signal and the multiplier input current signal are added to each other.

5. Current measurement apparatus according to claim 1 in which the current multiplier is configured such that the multiplier value is determined by a ratio of resistors, the ratio of resistors comprising a first resistor comprised in the first path and a second resistor comprised in the second path, with the relative values of the first and second resistors being set to provide a desired multiplier value.

6. Current measurement apparatus according to claim 5 in which at least one of the resistors which provides for the ratio of resistors comprises plural resistor elements.

7. Current measurement apparatus according to claim 6 comprising at least one switch which is operative to switch between different ones of the plural resistor elements, a duty cycle of switching being determined for one of resistor element degradation and resistor element matching.

8. Current measurement apparatus according to claim 5 in which at least one of the resistors which provides for the ratio of resistors is variable to thereby provide for change in the multiplier value, the variable resistor comprising plural resistor elements, the current multiplier comprising at least one switch which is operative to change a configuration of the plural resistor elements to thereby vary resistance.

9. Current measurement apparatus according to claim 5 in which the current multiplier comprises at least one switch and the at least one switch is operative to switch at least one of the resistors which provide for the ratio of resistors between two different resistance values to thereby modulate a signal received by the current multiplier.

10. Current measurement apparatus according to claim 5 in which the first and second resistors are electrically connected to an output of the current multiplier, the output of the current multiplier carrying a current signal which determines the reference input signal.

11. Current measurement apparatus according to claim 5 in which the current multiplier comprises a current source in the second path and the current multiplier is configured such that: the multiplier input current signal is received at a first end of the first resistor further from the measurement arrangement than the second, opposite end of the first resistor; and the second resistor is on a same side of the current source as the measurement arrangement.

12. Current measurement apparatus according to claim 11 in which the current multiplier comprises a comparison arrangement which is configured to compare a first voltage at the first end of the first resistor with a second voltage between the current source and the second resistor and provide a comparison output in dependence on the comparison, the current source being a controllable current source which is operative to vary its output current in dependence on the comparison output.

13. Current measurement apparatus according to claim 11 in which the current source comprises a transistor, one of a gate and base of the transistor constituting a control input of the current source.

14. Current measurement apparatus according to claim 1 in which the current multiplier comprises a current source in the second path and a first power supply provides power to the current source and a second power supply provides power to circuitry operative to provide the multiplier input current signal, a magnitude of the voltage of the first power supply being less than a voltage of the second power supply.

15. Current measurement apparatus according to claim 14 in which the current multiplier comprises a DC-DC converter which is operative to reduce a magnitude of a power supply voltage to the current source.

16. Current measurement apparatus according to claim 11 in which the current source comprises an inductor in series with the second resistor, an end of the inductor opposite an end of the inductor which is connected to the second resistor being switched between a high side of a power supply and a low side of the power supply.

17. Current measurement apparatus according to claim 16 in which the current multiplier comprises a comparator and a pulse width modulator, the comparator being configured to compare a first voltage at the first end of the first resistor with a second voltage between the current source and the second resistor and provide a comparator output in dependence on the comparison, the switching of the inductor being controlled by an output from a pulse width modulator which is controlled by the comparator output.

18. Current measurement apparatus according to claim 1 in which the reference input signal is between 100 μA and 500 mA and the load drawn current signal is at least 0.1 Amp peak or RMS.

19. Current measurement apparatus according to claim 1 in which the processing apparatus is operative to determine at least one of: a transfer function of the measurement apparatus; a change in a transfer function of the measurement apparatus; and the load drawn current signal further in dependence on the load output signal.

20. Current measurement apparatus according to claim 19 comprising at least one of: a voltage reference and in which the current measurement apparatus is configured such that the multiplier input current signal is dependent on an output from the voltage reference; a voltage to current converter and in which the c

Assignees

• Analog Devices Global

Inventors

• Hurwitz Jonathan Ephraim David
• Danesh Seyed Amir Ali
• Holland William Michael James

Classifications

• G01R17/02

  Arrangements in which the value to be measured is automatically compared with a reference value · CPC title

• G01R35/005

  Calibrating; Standards or reference devices, e.g. voltage or resistance standards, "golden" references (G01R33/0035, G01R35/002 take precedence) · CPC title

• G01R19/0092 Primary

  Measuring current only · CPC title