High-frequency coupler

1. A high-frequency coupler for extracting a secondary signal representative of a main signal carried by a conductive line, comprising two series-coupled, respectively high-pass and low-pass, filters, the input of which is intended to be connected to said line while its output is intended to provide the secondary signal, the filters being sized so that the sum of their respective attenuations is substantially constant over the coupler passband, and so that their respective cut-off frequencies are within said passband.

2. The coupler of claim 1 , wherein the sum of the respective attenuations of the filters is constant, plus or minus 10% on the coupler passband.

3. The coupler of claim 1 , wherein the coupling is of capacitive type.

4. The method of claim 3 , wherein the input of the high-pass filter is connected to the coupler input.

5. The coupler of claim 1 , wherein each filter comprises a single inductive and capacitive cell.

6. The coupler of claim 1 , formed as an integrated circuit.

7. The coupler of claim 1 , wherein the high-pass filter comprises a capacitor having a value comprised between 0.1 picofarad and 50 picofarads and an inductance having a value comprised between 0.1 nH and 50 nH.

8. The coupler of claim 1 , wherein the low-pass filter comprises a capacitor with a value comprised between 10 femtofarads and 100 picofarads and an inductance (L 2 ) with a value comprised between 0.1 nH and 50 nH.

9. The coupler of claim 1 , applied to the extraction of a signal for controlling a power amplifier of a radiofrequency transmission circuit.

10. A wideband radiofrequency transmission circuit comprising, between a transmit amplifier and an antenna, the coupler of claim 1 .

11. A portable phone comprising the circuit of claim 10 .