Method and device for amplifying a reception signal
View Patent ↗A method and a device for amplifying a reception signal are provided, involving the adjustment of a gain by which the reception signal is amplified, in particular as a function of a signal level of the reception signal. For example, lowpass filtering with a variable cutoff frequency is used to filter out a gain-dependent frequency range of the reception signal, which may especially contain an undesirable echo signal. Such a method and such a device are suitable in particular for the reception of ADSL signals in a central office.
1. A method of amplifying a reception signal in order to avoid overloading a subsequent signal processing unit, the method comprising adjusting a gain by which the reception signal is amplified, generating an amplified reception signal at the adjusted gain using an amplifier, and filtering out a gain-dependent frequency range of the reception signal when generating the amplified reception signal using a filter positioned in parallel with the amplifier, wherein the filtering step utilizes lowpass filtering with a gain-dependent cutoff frequency, and wherein the filtering step comprises lowering the cutoff frequency when the gain is increased and increasing the cutoff frequency when the gain is lowered.
2. The method of claim 1 , wherein the gain adjusting step includes adjusting the gain as a function of a signal level of the reception signal.
3. The method of claim 1 , wherein the generating step utilizes an operational amplifier to amplify the reception signal which operational amplifier has a feedback path comprising a parallel circuit having a capacitance and a variable resistance and further comprising varying the variable resistance to adjust the gain and the cutoff frequency.
4. The method of claim 1 , wherein the frequency range comprises a range of an echo signal contained in the reception signal.
5. The method of claim 1 , wherein the method is carried out to amplify an xDSL reception signal.
6. The method of claim 5 , further comprising receiving at a central office the xDSL reception signal from a subscriber connection and amplifying the received signal at the central office.
7. The method of claim 5 , wherein the method is carried out to amplify an ADSL reception signal.
8. An amplifier for amplifying a reception signal in order to avoid overloading a subsequent signal processing unit, the amplifier comprising an amplifier circuit coupled at an input to the reception signal for amplifying the reception signal to generate an amplified reception signal, a gain adjusting circuit coupled to the amplifier circuit and configured to adjust the gain by which the reception signal is amplified by the amplifier circuit, and a filter circuit coupled to the amplifier circuit in a feedback path comprising a parallel circuit including a capacitance and a variable resistance which when varied adjusts the gain and the cut-off frequency, the filter circuit configured to filter out a gain-dependent frequency range of the reception signal when generating the amplified reception signal, wherein the filter circuit is configured to provide lowpass filtering with a gain-dependent cutoff frequency, and wherein the filter circuit is configured to lower the cutoff frequency when the gain is increased and increase the cutoff frequency when the gain is lowered.
9. The device of claim 8 , further comprising a control circuit configured to adjust the gain as a function of a signal level of the reception signal.
10. The device of claim 8 , wherein the filter circuit comprises a lowpass filter.
11. The device of claim 8 , wherein the amplifier circuit comprises an operational amplifier.
12. The device of claim 11 , further comprising a feedback path coupled to the operational amplifier, the feedback path comprising a parallel circuit including a capacitance and a variable resistance which when varied adjusts the gain and the cut-off frequency.
13. The device of claim 12 , wherein the filter circuit comprises a low pass filter formed by the capacitance and variable resistance of the feedback path, further comprising a control circuit configured to adjust the gain of the amplifier as a function of a signal level of the reception signal, the control circuit being coupled to the variable resistance to vary the variable resistance to adjust both the gain and a cutoff frequency of the lowpass filter.
14. The device of claim 12 , wherein the variable resistance comprises a parallel circuit of a plurality of switchable resistors.
15. The device of claim 14 , wherein at least one of the plurality of switchable resistors is connected in series with a switch.
16. The device of claim 15 , wherein the switch comprise CMOS components.
17. The device of claim 15 , further comprising an input switch in an input path of the operational amplifier the input switch being configured to at least partially compensate for any effect on the gain due to the switch in the feedback path.
18. The device of claim 8 , wherein the device is configured for amplifying a differential input signal.