Battery monitoring circuit and method
A battery-monitoring circuit detects rapid changes in current drawn from a battery by a device powered thereby. The circuit includes calibrating operating modes that determine voltage-to-frequency conversion parameters, and amplifier errors at various levels of battery voltage.
1. A circuit for monitoring current supplied by a battery, the circuit comprising:
a detector including a resistor connected between the battery and a device powered thereby, and including a differential amplifier having inputs connected to terminals of the resistor for providing an output representative of current drawn by the device from the battery, the detector further comprising:
a reference resistor selectively connectable to the resistor;
a reference voltage; and
a switching circuit for selectively supplying the reference voltage to a series connection of the resistor and reference resistor for establishing a reference level of input to the differential amplifier;
a voltage-to-frequency converter coupled to receive the output from the detector for generating an output frequency proportional to the received output from the detector; and
a processor coupled to receive the output frequency from the voltage-to-frequency converter for producing an output representative of an integral of current over time drawn from the battery.
2. A circuit including a differential amplifier having inverting and non-inverting inputs for operation over a selected range of applied voltages, the circuit comprising:
a source of voltage at various amplitudes;
circuitry for connecting the source of voltage to the inverting and non-inverting inputs of the differential amplifier for supplying thereto a plurality of different voltages within the selected range;
a converter for converting an applied voltage to a corresponding frequency, the converter being connected to an output of the differential amplifier for producing output signals indicative of common-mode rejection error of the differential amplifier at each of the plurality of different voltages;
a memory communicating with the converter for storing frequency values representative of common-mode rejection errors at storage locations having addresses indicative of the corresponding plurality of different voltages within the selected range; and
a processor communicating with the memory and with the converter for producing an output representative of a correction by an amount of an error signal stored in the memory at an address location corresponding to a voltage at an input of the differential amplifier within the selected range, the processor controlling the circuitry for connecting the source of voltage to the differential amplifier or for connecting other voltages within the selected range to the inputs of the differential amplifier.
3. A circuit for monitoring current supplied by a battery, the circuit comprising:
a detector including a resistor connected between the battery and a device powered thereby, and including a differential amplifier having inputs connected to terminals of the resistor for providing an output representative of current drawn by the device from the battery, the detector also including a reference resistor selectively connectible to the resistor;
a reference voltage;
a switching circuit for selectively supplying the reference voltage to a series connection of the resistor and reference resistor for establishing a reference level of input to the differential amplifier;
a voltage-to-frequency converter coupled to receive the output from the detector for generating an output frequency proportional to the received output from the detector; and
a processor coupled to receive the output frequency from the voltage-to-frequency converter for producing an output representative of an integral of current over time drawn from the battery.
4. A method for operating an electronic circuit, including a differential amplifier having inverting and non-inverting inputs, the method comprising:
applying each of selected different voltages within a range of voltages to the inverting and non-inverting inputs of the differential amplifier to produce at an output thereof signals indicative of common-mode rejection errors at the corresponding selected applied voltages;
converting the error signals to associated frequency values;
storing the frequency values at memory locations having addresses indicative of the corresponding selected different voltages; and
retrieving a stored frequency value from a memory location at an address corresponding to a voltage applied to an input of the differential amplifier for logically combining with an output thereof to correct for common-mode rejection error of the differential amplifier.
5. A method for operating an electronic circuit, including a differential amplifier having inverting and non-inverting inputs, the method comprising:
applying each of selected different voltages within a range of voltages to the inverting and non-inverting inputs of the differential amplifier to produce at an output thereof signals indicative of common-mode rejection errors at the corresponding selected applied voltages;
converting the error signals to associated frequency values;
storing the frequency values at memory locations having addresses indicative of the corresponding selected different voltages; and
combining errors in converting error signals to associated frequency values with the errors indicative of common-mode rejection errors for storage at the memory locations having addresses indicative of the corresponding selected different voltages.
6. A circuit for monitoring current supplied by a battery, the circuit comprising:
a detector including a resistor connected between the battery and a device powered thereby, and including a differential amplifier having inputs connected to terminals of the resistor for providing an output representative of current drawn by the device from the battery, the detector also including a reference resistor selectively connectible to the resistor;
a reference voltage;
a switching circuit for selectively supplying the reference voltage to a series connection of the resistor and reference resistor for establishing a reference level of input to the differential amplifier, the switching circuit switching the resistor between the battery and the device in one mode, and applying the reference voltage to a series connection of the resistor and the reference resistor in another mode;
a voltage-to-frequency converter coupled to receive the output from the detector for generating an output frequency proportional to the received output from the detector; and
a processor coupled to receive the output frequency from the voltage-to-frequency converter for producing an output representative of an integral of current over time drawn from the battery.
7. A circuit for monitoring current supplied by a battery, the circuit comprising:
a detector including a resistor connected between the battery and a device powered thereby, and including a differential amplifier having inputs connected to terminals of the resistor for providing an output representative of current drawn by the device from the battery, the detector also including a reference resistor selectively connectible to the resistor;
a reference voltage;
a switching circuit for selectively supplying the reference voltage to a series connection of the resistor and reference resistor for establishing a reference level of input to the differential amplifier;
a voltage-to-frequency converter coupled to receive the output from the detector for generating an output frequency proportional to the received output from the detector;
a processor coupled to receive the output frequency from the voltage-to-frequency converter and calibrate a transform factor relating the output frequency of the voltage-to-frequency converter to the applied reference voltage for producing an output representative of an integral of current over time drawn from the battery.
8. A circuit for monitoring current supplied by a battery, the circuit comprising:
a detector including a resistor connected between the battery and a device powered thereby, and including a differential amplifier having inputs connected to terminals of the resistor for providing an output representative of current drawn by the device from the battery, the detector also including a reference resistor selectively connectible to the resistor;
a reference voltage;
a source of voltage variable over a range of voltages substantially representative of an operating range of battery voltages;
a switching circuit for selectively supplying the reference voltage to a series connection of the resistor and reference resistor for establishing a reference level of input to the differential amplifier, the switching circuit operable in a mode for connecting the source of variable voltage substantially in common to the inputs of the differential amplifier;
a voltage-to-frequency converter coupled to receive the output from the detector for generating an output frequency proportional to the received output from the detector; and
a processor coupled to receive the output frequency from the voltage-to-frequency converter for producing an output representative of an integral of current over time drawn from the battery.
9. The circuit of claim 8 in which the processor accumulates a voltage-to-frequency output for each of selected voltages from the source of variable voltages as error values at such selected voltages.
10. The circuit of claim 9 in which the switching circuit operable in another mode connects the resistor between the battery and the device; and
the processor alters by the error values the voltage to frequency output as a calibrated representation of current drawn by the device from the battery.