High pass filter with coefficient switching to improve settling time
AssigneeCrystal Semiconductor Corporation
InventorsKa Leung, Sarah Shuangxia Zhu
Life of this patent
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Abstract
A high pass filter is provided utilizing a digital filter with coefficients that can be switched to provide for two responses, a fast response and a slow response. A first response is provided by an accumulator block (38) disposed between the output and a summing junction (30) on the input of the digital filter. A multiplexer (40) selects between this accumulator block (38) and a slow response accumulator block (42). The switching is effected with a zero crossing detect circuit (26). When the first and faster response brings the DC level down to a value that is close to zero, the second and slower response is selected to basically lock it to zero.
Claims26
A high pass filter with a switched response, comprising:
- a first high pass filter section having a first response with a first time constant;
- a second high pass filter section having a second response with a second time constant, said second time constant longer than said first time constant;
- a detector for detecting when the output DC signal level of said high pass filter falls from a point above a predetermined DC signal level threshold to a point below said predetermined DC signal level threshold;
- and
- a switching device for switching said high pass filter between the response associated with said first high pass filter section and the response associated with said second high pass filter section, such that said first high pass filter section is utilized for signal levels above said predetermined DC signal level threshold and said switching device switches to said second high pass filter section when said detector detects a crossing of said predetermined DC signal level threshold from a point above said predetermined DC signal level threshold to a point therebelow.
A digital high pass filter, comprising:
- a digital filter for realizing a filter function;
- a coefficient memory for storing filter coefficients defining said filter function, said filter function having potentially first and second filter responses which are selectable;
- a detector for detecting when the DC signal level on the output of said digital filter is above or below a predetermined DC signal level threshold voltage;
- and
- a switch for controlling said digital filter to operate with said first filter response when the output signal level of said digital filter is on one side of said predetermined DC signal level threshold and with said second filter response when the output signal level of said digital filter is on the other side of said predetermined DC signal level threshold and wherein said first and second filter responses have different time constants.
A method for providing a high pass filter with a switched response, comprising the steps of:
- providing a first high pass filter section having a first response with a first time constant;
- providing a second high pass filter section having a second response with a second time constant, the second time constant longer than the first time constant;
- detecting when the output DC signal level of the high pass filter falls from a point above a pre-determined DC signal level threshold to a point below the pre-determined DC signal level threshold;
- and
- switching the high pass filter between the response associated with the first high pass filter section and the response associated with the second high pass filter section, such that the first filter section is utilized for signal levels above the pre-determined DC signal level threshold and the step of switching switches to the second filter section when the step of detecting detects a signal level crossing of the pre-determined DC signal level threshold from a point above the pre-determined DC signal level threshold to a point below the pre-determined DC signal level threshold, such that the second filter section is utilized for signal levels below the pre-determined DC signal level.
A method for providing a high pass filter, comprising the steps of:
- providing a digital filter for realizing a filter function;
- storing filter coefficients in a coefficient memory, the filter coefficients defining the filter function and the filter function having potentially first and second filter responses which are selectable;
- detecting when the DC signal level on the output of the high pass filter is above or below a pre-determined DC signal level threshold;
- and
- controlling the digital filter to operate with the first filter response when the output of the digital filter is on one side of the pre-determined DC signal level threshold and with the second filter response when the output of the digital filter is on the other side of the pre-determined DC signal level threshold and, wherein the first and second filter responses have different time constants.
Dependencies are inferred from the claim text.