Circuit feedback loop with monitored loop gain

Details Circuit feedback loop with monitored loop gain Circuit feedback loop with monitored loop gain

1998-02-27

1999-11-02

Pascal, Robert

Amplifiers

With amplifier condition indicating or testing means

330 75, 324123C, 4552261, G01R 1900, G01R 130, H03F 136, H04B 1700

Patent

active

059778245

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

This invention relates to a circuit arrangement comprising a feedback loop, which arrangement has a forward path for transmitting a result signal, a feedback path for deriving a feedback signal from the output signal of the forward path and a first re-combining stage for re-combining an input signal with the feedback signal to generate the result signal.
Such a circuit arrangement is known from European Patent Application 598 585. More particularly, the feedback loop described therein has the configuration of a Cartesian loop. Such Cartesian loops--but also feedback loops in more general terms--are to be used for a loop gain for the open feedback loop of which the gain value may at most have slight deviations from the set value for which the loop gain is designed. This is necessary for not affecting the stability of the loop and its bandwidth. In the known circuit arrangement, however, a measurement of the loop gain with open or interrupted feedback is not possible.


SUMMARY OF THE INVENTION

It is an object of the invention to provide a circuit arrangement of the type defined in the opening paragraph, in which the loop gain of the open loop can be measured and monitored without the transmission properties of the loop being affected.
According to the invention, this object is achieved with a circuit arrangement of this type by means of a measuring circuit for the production of a measuring signal, which signal is derived from the result signal and the feedback signal by linear combination.
An advantageous embodiment of the invention is characterized in that the measuring circuit comprises a first measuring signal path to which the result signal is applied and by which it is transmitted with a predefinable first transmission factor, a second measuring path to which the feedback signal is applied and by which the signal is transmitted with a predefinable second transmission factor, and also a second re-combining stage for additively combining the output signals of the measuring paths to form the measuring signal.
Preferably, the feedback loop is then arranged as a Cartesian loop.
Advantageously, the circuit arrangement according to the invention is used within an amplifier arrangement of a telecommunication apparatus.


BRIEF DESCRIPTION OF THE DRAWING

The drawing in which like elements are designated by like reference characters shows in:
FIG. 1 a block circuit diagram of a circuit arrangement according to the invention,
FIG. 2 a detailed embodiment of a measuring circuit for the circuit arrangement shown in FIG. 1, and
FIG. 3 shows an illustrative embodiment of the invention for a Cartesian loop.


DESCRIPTION OF THE PREFERRED EMBODIMENTS

The circuit arrangement shown in FIG. 1 comprises a forward path 1 shown as an amplifier stage having the gain factor G and whose input is connected to an output of a first re-combining stage 2 for the supply of a result signal. The first re-combining stage 2 is arranged as a subtracter, for example, a differential circuit (differential amplifier). In this first re-combining stage 2, a feedback signal is applied through a second input 4 and is subtracted from an input signal applied through a first input 3, i.e. additively re-combined in accordance with its sign. The feedback signal is generated by a feedback path 5 whose output is connected to the second input 4 of the first re-combining stage 2 and whose input is connected to the output of the forward path 1. An attenuator 6, in principle a part of the feedback path 5, is inserted in FIG. 1 into the link between the output of the forward path 1 and the input of the feedback path 5. For simplicity, however, it will be assumed in the following that the attenuator 6 forms a part of the feedback path 5 and that particularly its attenuation factor is incorporated in the transmission factor, i.e. the gain of the feedback path 5 which is referenced H in FIG. 1. Therefore, if a signal is available as a result signal on the output of the first re-combining stage 2, a signal eGH will appear on the o

REFERENCES:
patent: 5381108 (1995-01-01), Whitmarsh et al.
patent: 5793817 (1998-08-01), Wilson

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