Electrical filters enabling independent control of resonance of transisition frequency and of band-pass, especially for speech synthesizers

Claim 2

Electrical filter enabling independent control of resonance or transition frequency and of bandwidth which comprises an amplifier of gain G whose input is connected to two impedances Z1A and Z1B of a first type which are arranged in series with respect to the said input, have adjustable values and are such that the ratio between the value of the impedance Z1B connected directly to the input of the amplifier and the value of the other impedance Z1A is Z1B a Z1A, said amplifier being provided with a negative feedback loop between the output of the said amplifier and the junction between the two impedances Z1A and Z1B, two other impedances Z2A and Z2B of a second type which have adjustable values and are respectively connected in the negative feedback loop and connected between the input of the said amplifier and ground, being such that the ratio between the value of the impedance Z2B which is shunted across the input of the amplifier and the value of the other impedance Z2A is Z2B b Z2A, at least one of the two ratios a or b being substantially different from 1 and the ratios a and b and the gain G being connected by the relationship 1 + a - b (G-1) 0.

Claim 3

Electrical filter according to claim 1, of the resonating circuit type of which the transfer function comprises a complex pole, wherein the impedances of the first type are each constituted by an adjustable resistance and the impedances of the second type are each constituted by an adjustable resistance and a capacitor connected in parallel and the input of the filter is connected to the input of the amplifier of gain G through impedances of the first type and the output of this filter is constituted by the output of said amplifier.

Claim 4

Electrical filter according to claim 1, of the anti-resonant circuit type of which the transfer function comprises a complex zero, wherein the impedances of the first type are each constituted by an adjustable resistance and a capacitor connected in parallel and the impedances of the second type are constituted by an adjustable resistance and comprising a second amplifier of which the gain is of the order of the reciprocal 1/G of the first and of which the input is connected to the output of this amplifier of gain G, the output of this second amplifier being connected to the input of the amplifier of gain G through impedances of the first type, the input and the output of the filter being respectively constituted by the input and the output of this second amplifier.

Claim 5

Electrical filter according to claim 1, wherein the ratios a and b are substantially equal and have a value in the range between 1 and 20.

Claim 6

Electrical filter according to claim 1, wherein the ratios a and b are substantially equal and comprised between 1 and 20, and the overvoltage coefficient of the circuit comprising the amplifier of gain G and the impedances of the first and of the second type is greater than 5.

Claim 7

Electrical filter according to claim 1, wherein the impedances of the first and of the second type comprise only resistors and reactances of the capacitive type to the exclusion of all other impedance elements.

Claim 8

Electrical filter enabling independent control of resonance frequency and of bandwidth, comprising an amplifier whose gain G is of the order of three having an input connected to two impedances Z1A and Z1B of a first type arranged in series with respect to said input and having adjustable and substantially equal values, said amplifier being provided with a negative feedback loop between the output of said amplifier and the junction between said two impedances of the first type, two other impedances Z2A and Z2B of a second type, which have adjustable values and where Z2A is substantially equal to Z2B, said second type of impedances being respectively connected in the negative feedback loop and connected between the input of said amplifier and ground.

Claim 9

Electrical filter enabling independent control of resonance frequency and of bandwidth, comprising an amplifier whose gain G is of the order of three having an input connected to two impedances Z1A and Z1B of a first type arranged in series with respect to said input and having adjustable and substantially equal values, said amplifier being provided with a negative feedback loop between the output of said amplifier and the junction between said two impedances of the first type, two other impedances Z2A and Z2B of a second type, which have adjustable values and where Z2A is substantially equal to Z2B, said second type of impedances being respectively connected in the negative feedback loop and connected between the input of said amplifier and ground.

Claim 10

Electrical filter according to claim 7 of the anti-resonant circuit type having a transfer function comprising a complex zero, including a second amplifier whose gain is of the order of a third and whose input is connected to the output of said first amplifier, the output of said second amplifier being connected to the input of said first amplifier through the impedances Z1A and Z1B, the input and the output of the filter being respectively constituted by the input and the output of said second amplifier.

Claim 11

Electrical filter according to claim 8, wherein the impedances of the first type are each constituted by an adjustable resistance and a condenser connected in parallel to the exclusion of other types of impedance elements and the impedances of the second type are each constituted by an adjustable resistance to the exclusion of other types of impedance elements.

Claim 12

Electrical filter according to claim 7, wherein the impedances of the first and of the second type each include only real elements and reactive elements of the capacitive type to the exclusion of all other impedance elements.

Claim 13

Electrical filter according to claim 7, wherein the impedances of the first type are each constituted by an adjustable resistance to the exclusion of other types of impedance elements and the impedances of the second type are each constituted by an adjustable resistance and a condenser connected in parallel to the exclusion of other types of impedance elements.

Claim 14

Electrical filter according to claim 11, comprising control means independent of the cut-off frequency and of the bandwidth of the filter and adapted to adjust independently the average conductance of at least one of the resistances of the first and second type of impedance of the filter by periodically short-circuiting portions of each of these resistances at a frequency rate distinctly greater than the cut-off frequency of said filter and for periods dependent, for each type of impedance, on the value of a control signal.

Claim 15

Electrical filter according to claim 12, wherein at least one resistance of the first and second type of each impedance is divided into two partial resistances of which one is short-circuited as long as a switch connected to the terminals of the partial resistance mentioned receives an energising signal, and control means of the frequency of the filter which receive a control signal expressing, in analogue form and between given values, the value of the frequency (or of the bandwidth) comprise, a generator providing a saw-tooth signal of amplitude comprised between the above-said limits and having a constant period and, a comparator adapted to compare the control signal with the saw-tooth signal to provide to the switches, corresponding to one type of impedance, an energising signal as long as the saw-tooth signal has a value less than the control signal.

Claim 16

Electrical filter according to claim 12, wherein at least one resistance of the first and second type of impedance is divided into two partial resistances of which one is short-circuited as long as an electronic switch, connected to the terminals of the partial resistance mentioned, receives an energizing signal, and the means for controlling the frequency which receive a numerical control signal expressing in the form of parallel binary q signals the value of the frequency which value is capable of occupying 2q levels, comprise: a clock adapted to provide a train of pulses of given frequency and especially greater than the resonance frequency of the filter, a multistage counter adapted to count successively each group of 2q pulses issuing from the clock, a digital comparator adapted to compare the contents of the counter with the control signal, and flip-flop with Two control inputs coupled respectively to one stage of said counter and to said comparator, said flip-flop being placed in a first state, in which it provides through its output, to said electronic switch, energizing signals, when the counter counts the last pulse of each group of 2q pulses and being placed in its other state, for which the energizing signals are suppressed, when the comparator detects identity between the contents of the counter and the numerical control signal.

Claim 17

Electrical filter according to claim 7, wherein the impedances of the first type are each constituted by an adjustable resistance and a condenser connected in parallel to the exclusion of other types of impedance elements and the impedances of the second type are each constituted by an adjustable resistance to the exclusion of other types of impedance elements.

Claim 18

Electrical filter according to claim 7, wherein the impedances of the first type are each constituted by an adjustable resistance to the exclusion of other types of impedance elements and the impedances of the second type are each constituted by an adjustable resistance and a condenser connected in parallel to the exclusion of other types of impedance elements.