System and method for sensing an amplifier load current

• US 8,319,507 B2
• Filed: 02/08/2010
• Issued: 11/27/2012
• Est. Priority Date: 02/08/2010
• Status: Active Grant

• Current Assignee: NXP B.V. (NXP Semiconductors NV)
• Original Assignee: NXP B.V. (NXP Semiconductors NV)
• Inventors: Gautama, Temujin
• Primary Examiner(s): NGUYEN, HOAI AN D
• Application Number:
  US12/702,204
• Publication Number:
  US 20110193578A1
• Time in Patent Office: 1,023 Days
• Field of Search: 324/713, 324/691, 324/649, 324/600, 330/2, 702/107, 702/1, 702/57, 702/64
• US Class Current: 324/713
• CPC Class Codes: G01R 1/203 Resistors used for electric measuring, e.g. decade resistors standards, resistors for comparators, series resistors, shunts resistors in general H01C; microwave or radiowave terminations H01P1/26; coupling devices H01R
• CPC Class Codes: G01R 19/0092 measuring current only all subgroups of G01R19/00 take precedence
• CPC Class Codes: G01R 19/16528 using digital techniques or performing arithmetic operations using digital techniques to measure a voltage or a current, see G01R19/25
• CPC Class Codes: H03F 1/52 Circuit arrangements for protecting such amplifiers monitoring arrangements G01R31/28; increasing reliability in communication systems, e.g. using redundancy H04B1/74
• CPC Class Codes: H03F 2200/321 Use of a microprocessor in an amplifier circuit or its control circuit
• CPC Class Codes: H03F 2200/426 the amplifier comprising circuitry for protection against overload
• CPC Class Codes: H03F 2200/462 the current being sensed
• CPC Class Codes: H03F 3/187 in integrated circuits

Abstract

A system and method for sensing a load current that flows from an amplifier into a load of the amplifier involves obtaining a voltage drop across internal impedance of the amplifier and computing the load current using the internal impedance and the voltage drop across the internal impedance.

Claims

1. A method for sensing a load current that flows from an amplifier into a load of the amplifier, the method comprising:

obtaining a voltage drop across internal impedance of the amplifier; and

computing the load current using the internal impedance and the voltage drop across the internal impedance,

wherein obtaining the voltage drop across the internal impedance comprises;

generating a digital input voltage using a digital signal source;

converting the digital input voltage into an analog input voltage using a digital-to-analog converter;

applying the analog input voltage to the amplifier and generating an analog output voltage;

converting the analog output voltage into a digital output voltage using an analog-to-digital converter;

multiplying the digital input voltage by a gain factor of the amplifier to produce a voltage product using a digital signal processing module; and

calculating the voltage drop across the internal impedance as a voltage difference between the digital output voltage and the voltage product using the digital signal processing module.

2. The method of claim 1, wherein the voltage drop across the internal impedance, the load current, and the internal impedance are expressed as:

V=I*Z,

where V represents the voltage drop across the internal impedance, I represents the load current, * represents the convolution operator, and Z represents the internal impedance.

3. The method of claim 1, wherein the load current is sensed without measuring a voltage drop across a shunt resistor.

4. The method of claim 1, wherein the load of the amplifier comprises a loudspeaker.

5. The method of claim 2, wherein the internal impedance of the amplifier is frequency dependent.

6. The method of claim 2, wherein the internal impedance of the amplifier is a frequency independent resistance.

7. The method of claim 1, wherein the load current, the internal impedance, the voltage drop across the internal impedance, the digital input voltage, the digital output voltage, and the gain factor are expressed as:

V[k]=V_in[k]×

G−

V_out[k]=I[k]*Z[k],

where V[k] represents the voltage drop across the internal impedance in discrete time, k represents an index of discrete time, V_in[k] represents the digital input voltage, G represents the gain factor, V_out[k] represents the digital output voltage, I[k] represents the load current in discrete time, * represents the convolution operator, and Z[k] represents the internal impedance in discrete time.

8. A system for sensing a load current that flows from an amplifier into a load of the amplifier, the system comprising:

a voltage obtaining unit configured to obtain a voltage drop across internal impedance of the amplifier; and

a computing unit configured to compute the load current using the internal impedance and the voltage drop across the internal impedance,

wherein the voltage obtaining unit is further configured to;

generate a digital input voltage using a digital signal source;

convert the digital input voltage into an analog input voltage using a digital-to-analog converter;

apply the analog input voltage to the amplifier and generate an analog output voltage;

convert the analog output voltage into a digital output voltage using an analog-to-digital converter;

multiply the digital input voltage by a gain factor of the amplifier to produce a voltage product using a digital signal processing module; and

calculate the voltage drop across the internal impedance as a voltage difference between the digital output voltage and the voltage product using the digital signal processing module.

9. The system of claim 8, wherein the system does not include a shunt resistor in series with the load.

10. The system of claim 8, wherein the internal impedance of the amplifier is represented by a frequency independent resistance.

11. The system of claim 8, wherein the load of the amplifier comprises a loudspeaker.

12. The system of claim 8, wherein the voltage drop across the internal impedance, the load current, and the internal impedance are expressed as:

V=I*Z,

where V represents the voltage drop across the internal impedance, I represents the load current, * represents the convolution operator, and Z represents the internal impedance.

13. A system for sensing a load current that flows from an amplifier into a load of the amplifier, the system comprising:

a digital signal source configured to generate a digital input voltage;

a digital-to-analog converter configured to convert the digital input voltage into an analog input voltage, wherein the analog input voltage is applied to the amplifier to generate an analog output voltage;

an analog-to-digital converter configured to convert the analog output voltage into a digital output voltage; and

a digital signal processing module configured to multiply the digital input voltage by a gain factor of the amplifier to produce a voltage product, to calculate a voltage drop across internal impedance of the amplifier as a voltage difference between the digital output voltage and the voltage product, and to compute the load current using the voltage drop across the internal impedance.

14. The system of claim 13, wherein the load current, the internal impedance, the voltage drop across the internal impedance, the digital input voltage, the digital output voltage, and the gain factor are expressed as:

V[k]=V_in[k]×

G−

V_out[k]=I[k]*Z[k],

where V[k] represents the voltage drop across the internal impedance in discrete time, k represents an index of discrete time, V_in[k] represents the digital input voltage, G represents the gain factor, V_out[k] represents the digital output voltage, I[k] represents the load current in discrete time, * represents the convolution operator, and Z[k] represents the internal impedance in discrete time.

15. The system of claim 13, wherein the system does not include a shunt resistor in series with the load.

16. The system of claim 13, wherein the load of the amplifier comprises a loudspeaker.