Controllable circuit configuration for compensating fluctuations in an amplifier

#The invention relates to a controllable circuit configuration.

#The transmission properties of bipolar circuits, particularly in telephone circuit applications, are determined largely by discrete components such as resistors, capacitors and chokes. For instance, in speech circuits for telephone terminal devices, external resistors which are used to adjust the total amplification assure high accuracy and replicability that is independent of production variations, and they permit variation of the amplifications in the transmit and receive directions. One such circuit is known, for instance, from an article in the Siemens Data Book 1989/90, entitled ICs for Communication, PSB 4505/4506, pp. 782-811.

#In order to vary the amplification, the external components that are involved are typically replaced or recalibrated. However, that entails some effort, especially with later corrections. It would therefore be highly useful to set various parameters in as highly automated a way as possible, preferably under software control, especially for adapting the amplification and other parameters to the various regulations for telephone systems in various countries. In known circuit concepts, that is generally possible only at considerable additional expense for circuitry, and in particular it requires a greater number of external components.

#FIG. 1 is a schematic circuit diagram of a first, general embodiment of a circuit configuration according to the invention; and

#FIG. 2 is a circuit diagram of a second, more detailed embodiment of a circuit configuration according to the invention.

#Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is seen a circuit configuration according to the invention that includes a current-controlled amplifier CCA as a final control element, which is adjustable by a control current is in dependence on certain fluctuations and variations, and has a constant current source Q with an output current ia that is equally subject to the certain fluctuations and variations. The current-controlled amplifier CCA and the constant current source Q are integrated into a circuit IC1. These fluctuations in the current-controlled amplifier CCA and the constant current source Q are dependent on external influences, such as production-dictated variations and temperature. In order to bring these fluctuations into agreement, both of these components are integrated into a single circuit. Moreover, the elements that are definitive for the fluctuations in the current-controlled amplifier CCA and the constant current source Q are constructed identically, to the maximum possible extent. With integrated circuits, high absolute accuracy of electrical variables for individual elements can be achieved only at relatively major effort and expense, but high relative accuracy between two identically constructed elements can be achieved without major effort or expense.

#The output current ia of the constant current source Q is used to adjust the amplification of the current-controlled amplifier CCA. However, the output current ia is subject to production-dictated variation and therefore differs from one circuit to another. Since this current ia is in the same circuit as the control current is for adjusting the amplification of the current-controlled amplifier CCA, which is subject to the same production variations, the production variation averages out. In the same way, the temperature-dictated fluctuations of the constant current source Q and the current-controlled amplifier CCA cancel one another out. The output current ia of the constant current source Q and the control current is of the current-controlled amplifier CCA are linked together through a factor k. The amplification of the current-controlled amplifier CCA can be varied by varying the factor k.

#To this end, a multiplier MP1 is connected between the constant current source Q and the current-controlled amplifier CCA. The factor k depends on a control signal cs1 that is delivered to the multiplier MP1. The dependency between the control signal cs1 and the factor k may be arbitrary, and in the exemplary embodiment of FIG. 1 it is linear. The multiplier MP1, a further multiplier MP2 controlled by a control signal cs2 and a detector unit DT, are all integrated in a further circuit IC2. The two circuits IC1 and IC2 are joined together by bus lines BL1, BL2 and BL3. The bus line BL1 couples the inputs of the multipliers MP1 and MP2 and of the detector unit DT to the constant current source Q. The current output of the multiplier MP1 that carries the control current is is connected to a control input of the current-controlled amplifier CCA by the bus line BL2. The bus line BL3 connects a non-illustrated final control element of the integrated circuit IC1 to the current output of the multiplier MP2. This final control element may be a current-controlled amplifier, a current-controlled filter or a current-controlled oscillator. An input and an output of the current-controlled amplifier CCA and a current terminal of a controllable switch S that is connected between the constant current source Q and the bus line BL1, and which is likewise a component of the integrated circuit IC1, are also coupled to the further elements of the integrated circuit IC1. In the same way, other non-illustrated circuit elements of the integrated circuit IC2 are connected to an output of the detector unit DT and to control inputs of the multipliers MP1 and MP2. These further circuit elements also furnish the control signals cs1 and cs2. Through the use of the controlled switch S in combination with the detector unit DT, a signal that indicates the operational readiness of the integrated circuit IC1, for instance, can be transmitted from the integrated circuit IC1 to the integrated circuit IC2.