Calibration of a N-port receiver

Details Calibration of a N-port receiver Calibration of a N-port receiver

2000-07-07

2004-05-11

Bocure, Tesfaldet (Department: 2631)

Pulse or digital communications

Receivers

C375S344000, C375S224000

Reexamination Certificate

active

06735261

DESCRIPTION:
The solutions according to the present invention allow a simple calibration of N-port receivers, which are commonly used as IQ demodulators or direct demodulators of (n) PSK (n) QAM oscillator modulation schemes. Thereby a local oscillator is used as a RF source. After processing of the input RF signal originating from the local oscillator, calibration signals are provided to at least one of the inputs of the N-port receiver. This presents a simple technological solution to generate the required calibration signals only from the already available LO/RF source via an easy to implant passive circuitry. A more complicated generation of the calibration sequences (modulation, etc.) and an up-conversion block are no longer necessary. This calibration technique may cope with various effects like non-ideal matching of the power sensing devices, non-ideal matching of the associated gain block (providing RF/LF isolation) in very large passive element tolerances.
With reference to FIG. 1 a an embodiment of the present invention will be explained, wherein said embodiment is designed for an off-line calibration.
As shown in FIG. 1 a , the central elements are a calibration device 100 and a N-port structure 1 .In the usual operation, a RF signal originating from an antenna 17 is input to a first input 2 of the N-port structure 1 . A local oscillator RF signal originating from a local oscillator 4 is input to the second input 3 of the N-port structure 1 . As it is known from the prior art, the N-port structure (N being an integer larger than two) has N−2 terminals connected respectively to a power sensor 5 , 6 , 7 which supplies output signal respectively to a low filter 8 , 9 , 10 .The filtered output signal of the low pass filter 8 , 9 , 10 is supplied to an interface 11 and than to an analog digital post processing block 17 .
In case a calibration process is to be effected, a calibration control unit 15 controls switches 18 , 19 as the calibration device 100 such that the first RF input 2 and the second (LO) input 3 of the N-port structure are supplied by output signals of the calibration device 100 . The RF signal from the local oscillator 4 is supplied to the calibration device 100 . The calibration device 100 processes the RF signal from the local oscillator 4 and supplies calibration signals to the first RF input 2 and the second (LO) input 3 of the N-port structure 1 , respectively.
The calibration control unit 15 furthermore controls the calibration device 100 at a control terminal 18 .
When a calibration process is effected and the corresponding calibration signals are fed from the calibration device 100 to the first and second input 2 , 3 of the N-port structure 1 , the analog or digital post processing unit 17 detects the output signals of the low pass filter 8 , 9 , 10 and calculates calibration coefficients which are stored in a memory 16 . The analog or digital post processing unit 17 is also controlled by the calibration control unit 15 to switch from normal operation to calibration and vice versa. In the normal operation the analog or digital post processing unit 17 outputs detected IQ-values calculated on the basis of the output signals of the low pass filter 8 , 9 , 10 .
As can be seen from FIG. 1 a , the RF signal from the local oscillator 4 alone is the base for the calibration process and the calibration device 100 processes said RF signal from the local oscillator 4 , such that a calibration sequence generator in the baseband regime with subsequent up-conversion to the operation frequency is no longer necessary.
The interfaces necessary to connect the off-chip calibration devices are also shown in FIG. 1 a.
FIG. 1 b shows a modification of the scheme according to FIG. 1 a . According to the embodiment of FIG. 1 a the calibration process is controlled by an external calibration hardware 15 controlling a switch 18 and the calibration device 100 . Furthermore the external calibration hardware is connected to the memory 16 to store calculated calibration coefficients. To said effect to the external cali

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Ji Li et al: “A New Direct Digital Receiver Performing Coherent PSK Reception” IEEE MTT-S International Microwave Symposium Digest, Orlando, May 16-20, 1995, vol. 3, May 16, 1995, pp. 1007-1010, XP000552909.

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