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US 4,786,879 AGranted
Attenuator circuit employing bootstrapping
OwnerRay M. Dolbyinventor
Life of this patent
Estimating the term…
Abstract
When impedance elements such as FETs are used in attenuators, the elements have linear responses only when the signals attenuated are below certain signal levels. When signal conditions causing the element to operate non-linearly are detected, bootstrapping is applied to reduce the voltage across the element so that the element will operate linearly. The control signal at the gate of the element is then modified to compensate for the increase in effective impedance of the element caused by bootstrapping. The improved attentuators are especially useful in signal compressors and expanders.
Claims25
A circuit for attenuating signals comprising:
- a circuit element having a variable impedance for attenuating an input signal to obtain an attenuated output signal, said element having a first and second terminal and a control terminal, said input signal applied to the first terminal, wherein the impedance between the first and second terminals varies as a predetermined function of a first control signal applied to the control terminal when the voltage difference across the first and second terminals is less than a predetermined value;
- means for deriving a bootstrapping second control signal from the signal at a point in the circuit, said bootstrapping control signal for indicating a signal condition which causes the voltage across the first and second terminals to exceed said predetermined value, causing distortion in the output signal;
- and
- bootstrapping means responsive to the bootstrapping control signal for applying to the second terminal a fraction of the voltage at the first terminal when the bootstrapping control signal indicates said signal condition to reduce the voltage difference between the first and second terminals, where said fraction is of such magnitude that the voltage difference across the first and second terminals does not exceed the predetermined value.
1 more element
A device for modifying the dynamic range of an input signal within a frequency band, comprising:
- a first circuit having a fixed or sliding band characteristic action for compressing or expanding the dynamic range of input signal components;
- a second circuit including an impedance elements, said element having a variable impedance for attenuating an input signal, said element having a first and second terminal and a control terminal, said input signal applied to the first terminal, wherein the impedance between the first and second terminals varies as a predetermined function of a dynamic modification control signal applied to the control terminal when the voltage difference across the first and second terminals is less than a predetermined value;
- said second circuit having a sliding band characteristic action for compressing or expanding the dynamic range of signal components;
- means for coupling the output of the first circuit to the second circuit, so that the characteristic action of one circuit substitutes for the characteristic action of the other circuit in at least a portion of the frequency band;
- and
- bootstrapping means for applying to the second terminal a fraction of the voltage at the first terminal to reduce the voltage difference between the first and second terminals.
3 more elements
A device for modifying the dynamic range of input signals within a frequency band, comprising:
- a circuit including an impedance element, said element having a variable impedance for modifying the dynamic range of an input signal, said element having a first and second terminal and a control terminal, said input signal applied to the first terminal;
- means for applying a dynamic modification control signal to said control terminal, wherein the impedance between the first and second terminals varies as a function of the dynamic modification control signal applied to the control terminal when the voltage difference across the first and second terminals is less than a predetermined value;
- said circuit having a sliding band characteristic action for compressing or expanding the dynamic range of signal components;
- and
- bootstrapping means for applying to the second terminal a fraction of the voltage at the first terminal to reduce the voltage difference between the first and second
2 more elements
A circuit for modifying the dynamic range of an input signal, comprising:
- a main signal path which is substantially linear with respect to dynamic range, the main path receiving the input signal at its input;
- a further signal path which has its input derived from at least one point in the main path and its output signal combined with that of the main signal path to provide the output of the circuit;
- said further path comprising:
- (a) a frequency selective circuit determining a frequency pass-band within which the dynamic modification takes place, said input signal including both pass-band and stop-band signal components;
- (b) dynamic modification circuit means to effect progressive dynamic modification of signal components in that pass-band or to effect progressive sliding of the frequency pass-band, whereby the dynamic range is modified, the dynamic action of the dynamic modification circuit means being responsive to the pass-band signal components and the stop-band signal components within the circuit arrangement, wherein for high level input signals the dynamic action of the dynamic modification circuit means becomes less responsive to stop-band signal components;
- wherein the dynamic modification circuit means comprises a variable impedance element for effecting dynamic modification, said element having a first and a second terminal and a control terminal, the first and second terminals being in the further path so that the input signal to the further path is attenuated by the variable impedance of the element to provide an attenuated output signal for the further path, wherein the impedance between the first and second terminals varies as a predetermined function of a dynamic modification control signal generated in the dynamic modification circuit means and applied to the control terminal of the element, and wherein the element introduces distortion when the voltage between the first and second terminals exceeds a predetermined value;
- wherein at high level stop-band signal conditions, the dynamic action of the dynamic modification circuit means is such as to tend to increase the probability that the voltage across the first and second terminals exceeds the predetermined value;
- and
- (c) bootstrapping means for applying to the second terminal a fraction of the voltage at the first terminal so that the voltage difference between the first and second terminals does not exceed the predetermined value to reduce distortion.
6 more elements
Dependencies are inferred from the claim text.