Analog-to-digital converter having offset removing function
AssigneeBurr-Brown Corporation
InventorsMasayuki Ukawa, Hideki Kanayama
Life of this patent
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Abstract
In a delta-sigma type analog-to-digital converter, an offset varying during operation is removed, and a reduction in time required to generate a stable value after powering on the converter is achieved. A high pass filter is provided with a variable filter coefficient which can vary during operation. A filter coefficient controller supplies a coefficient control signal to the high pass filter to change the variable filter coefficient during operation, thereby altering the time constant of the high pass filter.
Claims19
A delta-sigma type analog-to-digital converter for receiving an analog input signal to generate a digital output signal representing the analog input signal in a digital form, comprising:
- (a) a delta-sigma type modulator connected to receive said analog input signal for generating a modulated output;
- (b) a decimation filter connected to receive said modulated output for generating a decimation filter output;
- (c) a high pass filter connected to receive said decimation filter output for generating a high pass filter output, said high pass filter having a variable filter coefficient during operation;
- and
- (d) a filter coefficient control circuit connected to said high pass filter for generating a coefficient control signal for specifying a change in said variable filter coefficient during operation, wherein
- the characteristic of said high pass filter is represented by using a Z function as follows:
- ##EQU5## where a.sub.l and b.sub.l are coefficients, and M and N are positive integers, and
- said variable filter coefficient includes a first filter coefficient comprising a first combination of values of a.sub.l and b.sub.l and a second filter coefficient comprising a second combination of values of a.sub.l and b.sub.l, said second combination being different from said first combination.
A delta-sigma type analog-to-digital converter for receiving an analog input signal to generate a digital output signal representing the analog input signal in a digital form, comprising:
- (a) a delta-sigma type modulator connected to receive said analog input signal for generating a modulated output;
- (b) a decimation filter connected to receive said modulated output for generating a decimation filter output;
- (c) a high pass filter connected to receive said decimation filter output for generating a high pass filter output, said high pass filter having a variable filter coefficient during operation;
- and
- (d) a filter coefficient control circuit connected to said high pass filter for generating a coefficient control signal for specifying a change in said variable filter coefficient during operation, wherein:
- said high pass filter is a first-order filter, said first-order filter having a characteristic represented by using a Z function as follows:
- ##EQU6## where k is a coefficient, and said variable filter coefficient produces a first filter coefficient comprising a first value of k and a second filter coefficient comprising a second value of k.
A delta-sigma type analog-to-digital converter for receiving an analog input signal to generate a digital output signal representing the analog input signal in a digital form, comprising:
- (a) a delta-sigma type modulator connected to receive said analog input signal for generating a modulated output;
- (b) a decimation filter connected to receive said modulated output for generating a decimation filter output;
- (c) a high pass filter connected to receive said decimation filter output for generating a high pass filter output, said high pass filter having a variable filter coefficient during operation;
- and
- (d) filter coefficient control means connected to said high pass filter for generating a coefficient control signal for specifying a change in said variable filter coefficient during operation.
A method of operating a delta-sigma analog-to-digital converter, comprising the steps of:
- (a) applying a power-on-reset signal to the analog-to-digital converter to reset functions of a delta-sigma modulator, decimation filter, and high pass filter of the delta-sigma analog-to-digital converter after electric power is applied to the delta-sigma analog-to-digital converter;
- (b) applying a first value of a coefficient control signal to the high pass filter to cause the high pass filter to have a first time constant;
- (c) after step (b), providing a DC dither signal in the delta-sigma modulator, the delta-sigma modulator, decimation filter, and high pass filter operating in response to the dither signal to produce a noise signal, the high pass filter operating to cause the noise signal to settle within an amount of time equal to the first time constant;
- (d) after the noise signal has settled, applying a second value of the coefficient control signal to the high pass filter to cause the high pass filter to have a second time constant that is substantially larger than the first time constant, and combining an analog input signal with the DC dither signal to produce a DC component including a DC bias signal and a DC offset of the delta-sigma modulator, the delta-sigma modulator, decimation filter, and high pass filter operating to convert the combined analog input signal and DC dither signal to a digital value wherein the high pass filter removes the DC component from an output of the decimation filter within an amount of time equal to the second time constant.
Dependencies are inferred from the claim text.