Automatic gain control unit for a low power receiver or transceiver, said receiver or transceiver comprising: - at least one antenna for receiving radio frequency signals, - at least one low noise amplifier for amplifying the signals received by the antenna, - a local oscillator for supplying oscillating signals, - at least one mixer unit for mixing the amplified incoming signals with the oscillating signals supplied by the local oscillator, in order to produce alternative intermediate signals, characterized in that the automatic gain control unit includes: - a first current source for charging or discharging by a first current at least one storage capacitor (Cc), - at least one comparator (11, 12, 13, 14) for comparing at least a first alternative intermediate signal among the alternative intermediate signals (Ip, In, Qp, Qn) and a first reference threshold, which is defined for a comparison with an upper side or a lower side of the first alternative intermediate signal to determine an amplitude level of the first alternative intermediate signal, - a gate controlled transistor (N1, N2, N3, N4) by an output of the comparator (11, 12, 13, 14), the transistor being conductive when the first alternative intermediate signal is greater than the first reference threshold for a comparison on the upper side, or lower than the first reference threshold for a comparison on the lower side, the transistor being connected in series between a second current source and the storage capacitor (Cc) in order to discharge or charge by a second current the storage capacitor inversely to the first current, the second current being supplied to the storage capacitor when the transistor is conductive, and the second current having a value greater than the first current, and - a bi-stable trigger element connected to the storage capacitor (Cc) and to provide an AGC signal depending on the voltage level on the storage capacitor for tuning the gain of the low noise amplifier or of a mixer unit amplifier. - at least one antenna for receiving radio frequency signals, - at least one low noise amplifier for amplifying the signals received by the antenna, - a local oscillator for supplying oscillating signals, - at least one mixer unit for mixing the amplified incoming signals with the oscillating signals supplied by the local oscillator, in order to produce alternative intermediate signals, - a first current source for charging or discharging by a first current at least one storage capacitor (Cc), - at least one comparator (11, 12, 13, 14) for comparing at least a first alternative intermediate signal among the alternative intermediate signals (Ip, In, Qp, Qn) and a first reference threshold, which is defined for a comparison with an upper side or a lower side of the first alternative intermediate signal to determine an amplitude level of the first alternative intermediate signal, - a gate controlled transistor (N1, N2, N3, N4) by an output of the comparator (11, 12, 13, 14), the transistor being conductive when the first alternative intermediate signal is greater than the first reference threshold for a comparison on the upper side, or lower than the first reference threshold for a comparison on the lower side, the transistor being connected in series between a second current source and the storage capacitor (Cc) in order to discharge or charge by a second current the storage capacitor inversely to the first current, the second current being supplied to the storage capacitor when the transistor is conductive, and the second current having a value greater than the first current, and - a bi-stable trigger element connected to the storage capacitor (Cc) and to provide an AGC signal depending on the voltage level on the storage capacitor for tuning the gain of the low noise amplifier or of a mixer unit amplifier.