Patent ID: 6496017
Filing Date: 2002-12-17
Classification: H04N

Abstract:
An arrangement for measuring an antenna signal strength (X), the arrangement comprising:a first amplifier section for receiving an antenna signal and for providing a first output signal, having a first automatic gain control stage with a first attenuation factor controlled by a first automatic gain control signal (VRF AGC); a second amplifier section for receiving a first input signal derived from said first output signal, for providing a second output signal, and having a second automatic gain control stage with a second attenuation factor controlled by a second automatic gain control signal (VIF AGC); automatic gain control means arranged to receive a second input signal (Vsync, top) derived from the second output signal and to generate said first and second automatic gain control signals in dependence on the second output signal; wherein:for values of said antenna signal below a predetermined threshold level (TOP), only said second automatic gain control stage may be active with an increasing second attenuation factor for increasing values of the antenna signal; for values of said antenna signal above said predetermined threshold level (TOP), said first automatic gain control stage is active with increasing first attenuation factor for increasing values of the antenna signal; wherein a processor is arranged to calculate said antenna signal strength (X) in accordance with the following steps:establishing whether or not said first automatic gain control stage is active; if said first automatic gain control stage is active, increasing said predetermined threshold level (TOP) to a first new threshold level such that said first new threshold level is equal to said antenna signal strength (X) and the first automatic gain control stage starts to become inactive, and calculating said antenna signal strength as being equal to said first new threshold level; and if said first automatic gain control stage is inactive, decreasing said predetermined threshold level (TOP) to a second new threshold level such that said second new threshold level is equal to said antenna signal strength (X) and the first automatic gain control stage starts to become active, and calculating said antenna signal strength as being equal to said second new threshold level.