Telecommunications – Receiver or analog modulated signal frequency converter – Noise or interference elimination
Patent
1995-08-02
1997-12-09
Vo, Nguyen
Telecommunications
Receiver or analog modulated signal frequency converter
Noise or interference elimination
455338, 329318, 329349, H04B 110
Patent
active
056970854
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an electrical device, more specifically, a radio transceiver comprising an arrangement for compensating for a DC component in an input signal to be processed, the compensating arrangement comprising means for forming the signal difference between the input signal and a DC compensation signal depending on a DC component found.
2. Discussion of the Related Art
When AC signals are processed, for example, in audio amplifiers, radio receivers and the like, the AC signal is processed in stages. To determine a specific DC operating point, the AC signal is converted in a processing stage to a specific DC level. For example, coupling capacitors or coupling transformers which pass only the AC component to the following stage are inserted between the processing stages.
Coupling capacitors and coupling transformers have a specific size especially when used with low frequencies. While circuit arrangements comprising resisters, diodes, transistors and so on can easily be integrated in large numbers in integrated circuits, the volume of a coupling capacitor having a large capacitance prevents cost-effective integration. Such coupling capacitors are therefore to be provided as external components outside the integrated circuit. This increases the cost of the modules, the cost of the components of the modules and the size of the modules. A further detrimental effect of coupling capacitors having a large capacitance as they are necessary, for example, in mobile radio receivers for baseband processing of time multiplex signals (capacitances in the .mu.F range) is that circuits comprising such large capacitors cannot be simply turned off after a receive burst of about 570 .mu.sec in length to save battery capacity during the receive pauses of about 4 msec. As a result of the large turn-on and turn-off time constants, the circuit would not be able to adjust to the new receive burst sufficiently fast. Thus the baseband circuit would have to remain turned on continuously, which reduces the operating time of the battery.
In integrated circuits the individual processing stages are normally DC coupled. This means that a DC component of the input signal to be processed (for example, from a baseband mixer) either reduces the useful dynamic range of the circuit, or even brings the circuit to saturation, so that no function can be executed any more.
For example, from the data sheet of the integrated circuit AD 7002, which sets out the baseband processing for the transmit and receive paths of a GSM radio telephone; a DC compensation arrangement component comprising a digital offset register is known to compensate for an input voltage offset. A DC value measured during a calibration cycle is stored separately for each filter input of the IC in the digital offset register. The value of the DC component stored in the corresponding register is subtracted from the corresponding filter output signal during a cycle of normal operation. This measurement is to be repeated at least when the integrated circuit is initially used and, if a fluctuation of the DC component cannot be excluded, for example, as a result of temperature influences, at regular intervals. For a measurement during the calibration cycle, however, the input signal cannot be used, so that only the DC component is measured which is available even if there is no input signal. Neither is it possible to use the IC during the calibration operation.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a device of the type defined in the opening paragraph in which a compensation is effected for the DC component contained in the input signal even when the device is in operation without any effect on the function of the device. In addition, the arrangement for compensating for the DC component is to be suitable both for discrete and for integrated structures.
In a device of the type defined in the opening paragraph this object is achieved in that the arrangement for compensating for the DC
REFERENCES:
patent: 5175749 (1992-12-01), Ficht et al.
patent: 5212826 (1993-05-01), Rabe et al.
patent: 5241702 (1993-08-01), Dent
patent: 5422889 (1995-06-01), Sevenhans et al.
Birth Winfrid
Saur Erich
Schaier Arthur G.
U.S. Philips Corporation
Vo Nguyen
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