Receiver arrangement with AC coupling
View Patent ↗A receiver arrangement with AC coupling is specified in which a filter arrangement ( 3 ) is provided in a baseband signal processing chain in a homodyne receiver and can be switched between at least two high-pass filter cut-off frequencies. In this case, a brief changeover is made to a higher cut-off frequency when varying the gain of a low-noise baseband amplifier ( 2 ), for example when the received field strength changes, during the reception mode. The described arrangement allows changes to be carried out to the gain in baseband during the normal reception mode. The present receiver is accordingly suitable for code division multiple access methods, such as those which are provided in the UMTS Standard.
1. A receiver arrangement with AC coupling, comprising:
an input of the receiver arrangement configured to receive a radio-frequency signal;
a frequency converter which is coupled to the input of the receiver arrangement and produces a baseband signal at its output;
a baseband amplifier with variable gain, which is connected to the output of the frequency converter and has a control input for varying the gain;
a filter arrangement for AC coupling, with an input which is connected to an output of the baseband amplifier and with a high-pass filter for filtering the baseband signal, with a cut-off frequency which can be switched between at least two values, with the lower of the at least two cut-off frequencies being used during normal operation and with the higher of the at least two cut-off frequencies being used in a changeover mode, and with a control input for varying the cut-off frequency; and
a control circuit for activation of the higher cut-off frequency during the changeover mode on the basis of a readjustment of the gain of the baseband amplifier, with an output which is connected to the control inputs of the baseband amplifier and of the filter arrangement,
wherein the control circuit is configured to activate the higher cut-off frequency in the high-pass filter of the filter arrangement during a variable time interval, which starts at the time of the change to the gain of the baseband amplifier on the basis of the readjustment of the gain.
2. The receiver arrangement as claimed in claim 1 , wherein the filter arrangement comprises a selectively activatable low-pass filter coupled to the control circuit in order to activate the low-pass filter effect during the changeover mode.
3. The receiver arrangement as claimed in claim 2 , including a programmable amplifier coupled to the output of the filter arrangement and connected to the control circuit, in order to set the lowest gain which can be set for the programmable amplifier during the changeover mode.
4. The receiver arrangement as claimed in claim 1 , including a programmable amplifier coupled to the output of the filter arrangement and connected to the control circuit, in order to set the lowest gain which can be set for the programmable amplifier during the changeover mode.
5. The receiver arrangement as claimed in claim 1 , wherein the filter arrangement comprises a selectively activatable low-pass filter coupled to the control circuit in order to activate the low-pass filter effect during the changeover mode.
6. The receiver arrangement as claimed in claim 5 , including a programmable amplifier coupled to the output of the filter arrangement and connected to the control circuit, in order to set the lowest gain which can be set for the programmable amplifier during the changeover mode.
7. The receiver arrangement as claimed in claim 1 , including a programmable amplifier coupled to the output of the filter arrangement and connected to the control circuit, in order to set the lowest gain which can be set for the programmable amplifier during the changeover mode.
8. The receiver arrangement as claimed in claim 7 , including a baseband filter for channel selection connected between the filter arrangement and the programmable amplifier.
9. The receiver arrangement as claimed in claim 1 , wherein the receiver arrangement is designed for processing balanced signals.
10. The receiver arrangement as claimed in claim 1 , wherein the high-pass filter in the filter arrangement comprises a balanced signal path having therein a parallel branch that includes a resistor and a parallel-connected first switch, the balanced signal path including series branches connected upstream of the parallel branch, each said series branch including a capacitance.
11. The receiver arrangement as claimed in claim 10 , including a baseband filter for channel selection connected between the filter arrangement and the programmable amplifier.
12. The receiver arrangement as claimed in claim 10 , including a programmable amplifier coupled to the output of the filter arrangement and connected to the control circuit, in order to set the lowest gain which can be set for the programmable amplifier during the changeover mode.
13. The receiver arrangement as claimed in claim 10 , wherein the filter arrangement comprises a selectively activatable low-pass filter coupled to the control circuit in order to activate the low-pass filter effect during the changeover mode.
14. The receiver arrangement as claimed in claim 13 , including a programmable amplifier coupled to the output of the filter arrangement and connected to the control circuit, in order to set the lowest gain which can be set for the programmable amplifier during the changeover mode.
15. The receiver arrangement as claimed in claim 10 , including a programmable amplifier coupled to the output of the filter arrangement and connected to the control circuit, in order to set the lowest gain which can be set for the programmable amplifier during the changeover mode.
16. The receiver arrangement as claimed in claim 10 , wherein the filter arrangement comprises a selectively activatable low-pass filter coupled to the control circuit in order to activate the low-pass filter effect during the changeover mode.
17. The receiver arrangement as claimed in claim 16 , including a programmable amplifier coupled to the output of the filter arrangement and connected to the control circuit, in order to set the lowest gain which can be set for the programmable amplifier during the changeover mode.
18. The receiver arrangement as claimed in claim 10 , wherein the series branches of the balanced signal path in the filter arrangement each comprise a parallel circuit formed by a resistor and a second switch in order to form with the associated capacitance a low-pass filter, and wherein the parallel circuits are connected upstream of the associated capacitances.
19. The receiver arrangement as claimed in claim 18 , wherein the parallel branch includes a further resistor and parallel-connected first switch, connected in series with the first-mentioned resistor and parallel-connected first switch, and wherein the control circuit is operable such that in order to activate the changeover mode, the second switches are first of all opened and the first switches are then closed, and such that, in order to return to the normal mode, the first switches are first of all opened, and the second switches are then closed.
20. The receiver arrangement as claimed in claim 1 , wherein the higher cut-off frequency is greater than or equal to 1 Megahertz.