Circuit for tuning an active filter
First Claim
1. A circuit includingan active filter having a plurality of first linear electronic elements arranged as a switchable array and at least one second linear electronic element, the first linear electronic elements having an electrical characteristic represented by a first design value and the second linear electronic element having an electrical characteristic represented by a second design value, the first and second linear electronic elements substantially determining a time constant of the active filter, and a tuning circuit for outputting a digital code n to the array of first linear electronic elements to adjust the time constant of the active filter approximately to a predefined value, the tuning circuit comprising:
- a first linear tuning element having an electrical characteristic represented by the first design value times a first predefined factor KC;
a second linear tuning element having an electrical characteristic represented by the second design value times a second predefined factor KR;
a signal generator configured to generate a signal indicative of a tuning time constant determined by the first and second linear tuning elements;
a backward counter having a reset input configured to reset the backward counter upon receipt of a reset signal to an initial value xmax that includes a relationship of the time constant of the active filter circuit and the tuning time constant;
a clock input connected to receive a clock signal, an enable input connected to the signal generator to receive a signal for starting the counter with the initial value xmax and stopping the counter in order to generate a count value xn, and a counter output configured to provide the count value xn; and
a decoder configured to convert the count value xn into a digital code n for switching the array of first linear electronic elements.
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Accused Products
Abstract
A circuit comprises an active filter with linear elements and a tuning circuit with linear elements of the same type as the filter circuit. A backward counter generates a count value that represents a time constant of the tuning circuit. The initial value of the backward counter contains information concerning the relationship between the time constant of the filter circuit and the tuning circuit. A decoder creates a digital code responsive to the count value which is used to switch an array of linear elements in order to tune the time constant of the filter to approximately a desired design value.
111 Citations
30 Claims
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1. A circuit including
an active filter having a plurality of first linear electronic elements arranged as a switchable array and at least one second linear electronic element, the first linear electronic elements having an electrical characteristic represented by a first design value and the second linear electronic element having an electrical characteristic represented by a second design value, the first and second linear electronic elements substantially determining a time constant of the active filter, and a tuning circuit for outputting a digital code n to the array of first linear electronic elements to adjust the time constant of the active filter approximately to a predefined value, the tuning circuit comprising: -
a first linear tuning element having an electrical characteristic represented by the first design value times a first predefined factor KC;
a second linear tuning element having an electrical characteristic represented by the second design value times a second predefined factor KR;
a signal generator configured to generate a signal indicative of a tuning time constant determined by the first and second linear tuning elements;
a backward counter having a reset input configured to reset the backward counter upon receipt of a reset signal to an initial value xmax that includes a relationship of the time constant of the active filter circuit and the tuning time constant;
a clock input connected to receive a clock signal, an enable input connected to the signal generator to receive a signal for starting the counter with the initial value xmax and stopping the counter in order to generate a count value xn, and a counter output configured to provide the count value xn; and
a decoder configured to convert the count value xn into a digital code n for switching the array of first linear electronic elements. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A circuit including
an active filter having a plurality of first linear electronic elements at least some of which are arranged as a switchable array and a second linear electronic element, each of the first linear electronic elements corresponding to a first design value and the second linear electronic element corresponding to a second design value, the first and second linear electronic elements substantially determining a time constant of the active filter, a first linear tuning element having an electrical characteristic determined by the first design value; -
a second linear tuning element having an electrical characteristic determined by the second design value;
the first and second tuning element defining a tuning time constant;
means for generating a signal indicative of the tuning time constant;
means for providing an output count value on the basis of an initial count value representing a relationship between the time constant and the tuning time constant; and
means for providing a digital code to the switchable array on the basis of the output count value in order to adjust the time constant. - View Dependent Claims (20, 21, 22)
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23. A method of tuning an active filter, the active filter comprising a plurality of first linear electronic elements at least some of which are arranged as a switchable array, and a second linear electronic element, each of the first linear electronic elements corresponding to a first design value and the second linear electronic element corresponding to a second design value, the first and second linear electronic elements substantially determining a time constant of the active filter, the method comprising:
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generating a signal indicative of a tuning time constant defined by a first linear tuning element and a second linear tuning element, wherein an electrical characteristic of the first linear tuning element is determined by the first design value, and an electrical characteristic of the second linear tuning element is determined by the second design value;
starting and stopping, on the basis of said signal, a counter operated at a clock frequency to generate a count value, wherein an initial count value of the counter is determined by the time constant and the tuning time constant. - View Dependent Claims (24, 25, 26, 27, 28, 29, 30)
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Specification