Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – By periodic switching
Reexamination Certificate
1999-11-05
2001-06-19
Cunningham, Terry D. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
By periodic switching
C327S175000, C327S176000, C327S355000, C327S408000
Reexamination Certificate
active
06249158
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a circuit arrangement for generating an output signal at an output by combining first and a second input signal, comprising at least a controllable switches for applying a respective one of the input signals to the output, in which, for the purpose of switching the output from one of the input signals to the other, a first one of the controllable switches is gradually switched from the blocked to the conducting state, and a second one of the controllable switches is switched complementarily thereto from the conducting to the blocked state.
2. Description of the Related Art
German Patent DE 32 00 071 A1 corresponding to U.S. Pat. No. 4,430,609 discloses a signal transmission device with a transmission characteristic which is adjustable in steps, comprising at least a group of controllable switches for applying a signal at various inputs to an output. This signal transmission device comprises control means with which one of the switches is, each time, rendered conducting, these switches being rendered conducting and non-conducting by means of a control signal. A control signal generator is provided for generating a first control signal which changes uniformly with respect to time and, by means of which, a given switch of the afore-mentioned group of controllable switches is gradually rendered conducting, and for generating a second control signal which is complementary to the first control signal, this second control signal simultaneously and uniformly rendered, non-conducting another switch of this group. The described operation of switching the switches or changing the control signals may be performed stepwise.
German Patent DE 196 35 050 A1 corresponding to U.S. Pat. No. 5,963,081, discloses a circuit arrangement having at least two signal paths which can each be fed by a controllable current source and are alternately switched to activity by means of logic signals selecting one of the controllable current sources. When changing over from one signal path to another during a transition interval, the controllable current sources of the relevant two signal paths are to be controlled by a temporally constantly changing control signal in such a way that currents, which can be supplied by these two controllable current sources, change constantly and with opposite sense. In accordance with German Patent DE 196 35 050 A1, a device, with which a gradual transition from one adjusting position to the next is achieved, is embodied by a control circuit comprising a control stage for each signal path. Each control stage comprises an analog multiplex branch via which the current activating the controllable current source associated with the relevant signal path, can be derived from a reference current source comprised in the control circuit and being common for the multiplex branches of all control stages. Moreover, each control stage has a bistable stage for constant control of the current in the multiplex branch in dependence upon the control signal, and for storing the state of operation of the multiplex branch achieved at the end of the transition interval outside the transition interval, as well as a switching stage for switching the control signal during the transition interval by means of the logic signals via the bistable stage to the multiplex branch of that signal path which, after termination of the transition interval, is to be activated in dependence upon the logic signals.
In the known circuit arrangements, fading between the signals at the various outputs for forming the output signal is performed by way of an “analog” switching operation. In this analog switching operation, the control characteristic of the components used for switching is an essential factor of influence. Due to inaccuracies of these control characteristics, particularly due to tolerance deviations and inaccurate matching of the characteristics with each other, distortions may occur which become manifest during fading, particularly in the case of large signal differences. These distortions may noticeably affect the reproduction quality of the output signal. Particularly, when such a circuit arrangement is used for volume control in audio signal reproducing devices, these distortions may become audible and thus deteriorate the aural impression.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a circuit arrangement of the type described, avoiding distortions caused by tolerances and inaccuracies in matching the characteristics of the components used for switching, and this with a small number of components.
According to the invention, this object is achieved in a circuit arrangement according to the invention in that the controllable switches are switched oppositely to each other between their completely conducting and their completely blocked state with a mutually complementary, gradually changed duty cycle.
In accordance with the invention, the controllable switches, provided as components for the switching operation, are thus alternately and constantly rendered fully conducting or fully blocked. Since the central range of characteristics of these components between the two mentioned states for gaining the output signal from the input signals applied via the controllable switches thus does not play a role, non-linearities in this central range of characteristics or an inadequately complementary matching with each other cannot affect the operational behavior of the circuit arrangement according to the invention. Also, when using components having an insufficient linearity in the central range of characteristics or an insufficient matching with each other, a correct switching without signal errors can be achieved.
Based on these advantageous properties in switching the output of the circuit arrangement between two input signals, the circuit arrangement according to the invention may also be used for a static adjustment of a linear combination of at least two input signals and not only for a dynamic switching of the output from one of the input signals in a first static state to a second input signal in a second static state. A linear combination of more than two input signals is also possible, in which case, a corresponding number of controllable switches are switched, complementary to each other, between their fully conducting state and their fully blocked state in an opposite sense, so that at any instant, only one of the switches is conducting and the others are blocked.
In the case of a static adjustment of a linear combination of two or more input signals, the duty cycle with which the controllable switches are switched remains temporally constant.
In an advantageous embodiment, the output of the circuit arrangement, according to the invention, is connected to an integration arrangement for integrating, or low-pass filtering, the output signal. Those signal components which occur in the output signal due to switching of the controllable switches, can be filtered from this output signal by this integration arrangement. These signal components can then no longer influence a further processing of the output signal.
In another embodiment of the circuit arrangement according to the invention, the output is switched from one of the input signals to the other within a switching interval having a predeterminable duration. The duty cycle of the associated controllable switches is then gradually raised complementary to each other from zero to 100% or reduced from 100% to zero within this switching interval. The duration of the switching interval may be preferably adjustable, and advantageously, has a value of ≦1 msec or ≧20 msec.
In another embodiment, the circuit arrangement according to the invention comprises a control arrangement for generating two mutually complementary control signals for complementarily switching the controllable switches. These control signals are particularly constituted by pulse density or pulse frequency-controlled pulse signals.
It appears that the control of the pulse density or p
Bradinal Werner
Nieke Norbert
Schillhof Udo
Cunningham Terry D.
Goodman Edward W.
Tra Quan
U.S. Philips Corporation
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