Amplifier system for cell sites and other suitable applications
In one embodiment, an amplifier system has a tap, a delay filter, a linearized amplifier, and a hybrid combiner. The tapped portion of an input signal is amplified by the amplifier, the untapped portion of the input signal is delayed by the delay filter, and the combiner combines the resulting amplified, tapped portion and the delayed, untapped portion to generate an amplified output signal. By re-combining the delayed, untapped portion of the input signal with the amplified, tapped portion, the power of the untapped portion is not lost, and the amplifier does not have to compensate for all of the distortion that would otherwise be associated with the total output power level. Such an amplifier system is applicable, for example, in upgrading an existing GSM cell site to support both GSM communications as well as UMTS communications without degrading GSM operations.
1. Apparatus having an amplifier system comprising:
a tap adapted to split an amplifier input signal into a tapped signal and an untapped signal;
an all-pass delay filter adapted to delay the untapped signal to generate an undivided, full-bandwidth, delayed version of the amplifier input signal;
an amplifier adapted to amplify the tapped signal to generate an undivided amplified version of the amplifier input signal, wherein the undivided amplified version of the amplifier input signal is in phase with the undivided, full-bandwidth, delayed version of the amplifier input signal; and
a combiner adapted to coherently add the undivided, full-bandwidth, delayed version of the amplifier input signal and the undivided amplified version of the amplifier input signal to generate an amplified output signal having a power dependent upon the sum of the powers of the undivided, full-bandwidth, delayed version and the undivided amplified version of the amplifier input signal, wherein the amplifier is a linearized amplifier that comprises:
a phase shifter;
first and second amplifiers connected in a cross cancellation configuration; and
a third amplifier connected to provide feed forward distortion compensation for the first and second amplifiers.
2. A method for upgrading an existing cell site that supports communications of two different sets of downlink/uplink signals to be an upgraded cell site that supports communications of at least three different sets of downlink/uplink signals, wherein the existing cell site applies (i) a first downlink signal to a first antenna of the existing cell site and (ii) a second downlink signal to a second antenna of the existing cell site, the method comprising:
(a) configuring the cell site to generate a third downlink signal; and
(b) configuring the cell site with an interface unit comprising:
a combiner adapted to combine two of the downlink signals to generate a combined downlink signal; and
an amplifier system adapted to amplify the combined downlink signal to generate an amplified combined downlink signal, wherein:
the interface unit is connected to apply (i) the amplified combined downlink signal to the first antenna and (ii) a remaining downlink signal to the second antenna; and
the amplifier system comprises:
a tap adapted to split the combined downlink signal into a tapped signal and an untapped signal;
an all-pass delay filter adapted to delay the untapped signal to generate an undivided, full-bandwidth, delayed version of the amplifier input signal;
an amplifier adapted to amplify the tapped signal to generate an undivided amplified version of the amplifier input signal, wherein the undivided amplified version of the amplifier input signal is in phase with the undivided, full-bandwidth, delayed version of the amplifier input signal, wherein the amplifier comprises:
first and second amplifiers connected in a cross cancellation configuration; and
a third amplifier connected to provide feed forward distortion compensation; and
a combiner adapted to coherently add the undivided, full-bandwidth, delayed version of the amplifier input signal and the undivided amplified version of the amplifier input signal to generate the amplified combined downlink signal having a power dependent upon the sum of the powers of the undivided, full-bandwidth, delayed version and the undivided amplified version of the amplifier input signal.
3. The method of claim 2 , wherein:
the existing cell site is a GSM cell site having a GSM BTS;
the first and second downlink signals are two different GSM downlink signals generated by the GSM BTS;
step (a) comprises configuring the cell site with a UMTS BTS; and
the third downlink signal is a UMTS downlink signal generated by the UMTS BTS.
4. The method of claim 2 , wherein:
the tap is an approximately −10 dB coupler;
the amplifier system applies a gain of about 13 dB; and
the combiner is a 3:1 combiner, such that the amplified combined downlink signal's power level is about twice the combined downlink signal's power level.
5. A cell site comprising an interface unit connected to one or more BTSs and at least first and second antennas, wherein the interface unit comprises:
a combiner adapted to combine first and second downlink signals received from the one or more BTSs to generate a combined downlink signal; and
an amplifier system adapted to amplify the combined downlink signal to generate an amplified combined downlink signal, wherein:
the interface unit is connected to apply (i) the amplified combined downlink signal to the first antenna and (ii) a third downlink signal received from the one or more BTSs to the second antenna; and
the amplifier system comprises:
a tap adapted to split the combined downlink signal into a tapped signal and an untapped signal;
an all-pass delay filter adapted to delay the untapped signal to generate an undivided, full-bandwidth, delayed version of the amplifier input signal;
an amplifier adapted to amplify the tapped signal to generate an undivided amplified version of the amplifier input signal, wherein the undivided amplified version of the amplifier input signal is in phase with the undivided, full-bandwidth, delayed version of the amplifier input signal, wherein the amplifier is a linearized amplifier comprising:
a phase shifter;
first and second amplifiers connected in a cross cancellation configuration; and
a third amplifier connected to provide feed forward distortion compensation for the first and second amplifiers; and
a combiner adapted to coherently add the undivided, full-bandwidth, delayed version of the amplifier input signal and the undivided amplified version of the amplifier input signal to generate the amplified combined downlink signal having a power dependent upon the sum of the powers of the undivided, full-bandwidth, delayed version and the undivided amplified version of the amplifier input signal.
6. The cell site of claim 5 , wherein:
the one or more BTSs comprise a GSM BTS and a UMTS BTS;
the first and second downlink signals are two different GSM downlink signals generated by the GSM BTS; and
the third downlink signal is a UMTS downlink signal generated by the UMTS BTS.
7. The cell site of claim 5 , wherein:
the tap is an approximately −10 dB coupler;
the amplifier system applies a gain of about 13 dB; and
the combiner is a 3:1 combiner, such that the amplified combined downlink signal's power level is about twice the combined downlink signal's power level.
8. Apparatus having an amplifier system comprising:
a tap adapted to split an amplifier input signal into a tapped signal and an untapped signal;
a delay filter adapted to delay the untapped signal to generate a delayed version of the amplifier input signal;
an amplifier adapted to amplify the tapped signal to generate an amplified version of the amplifier input signal, wherein the amplified version of the amplifier input signal is in phase with the delayed version of the amplifier input signal; and
a combiner adapted to coherently add the delayed version of the amplifier input signal and the amplified version of the amplifier input signal to generate an amplified output signal having a power dependent upon the sum of the powers of the delayed version and the amplified version of the amplifier input signal, wherein:
the tap is an approximately −10 dB coupler;
the amplifier applies a gain of about 13 dB; and
the combiner is a 3:1 combiner, such that the amplified output signal's power level is about twice the input signal's power level, when losses in the tap, the delay filter, and the combiner are taken into account.
9. The apparatus of claim 8 , wherein the amplifier is a linearized amplifier that includes a phase shifter.
10. The apparatus of claim 9 , wherein the linearized amplifier comprises:
first and second amplifiers connected in a cross cancellation configuration; and
a third amplifier connected to provide feed forward distortion compensation for the first and second amplifiers.
11. Apparatus having an amplifier system comprising:
a tap adapted to split an amplifier input signal into a tapped signal and an untapped signal;
a delay filter adapted to delay the untapped signal to generate a delayed version of the amplifier input signal;
an amplifier adapted to amplify the tapped signal to generate an amplified version of the amplifier input signal, wherein the amplified version of the amplifier input signal is in phase with the delayed version of the amplifier input signal; and
a combiner adapted to coherently add the delayed version of the amplifier input signal and the amplified version of the amplifier input signal to generate an amplified output signal having a power dependent upon the sum of the powers of the delayed version and the amplified version of the amplifier input signal, wherein the amplifier is a linearized amplifier comprises:
a phase shifter;
first and second amplifiers connected in a cross cancellation configuration; and
a third amplifier connected to provide feed forward distortion compensation for the first and second amplifiers.
12. The apparatus of claim 11 , wherein:
the tap is an approximately −10 dB coupler;
the amplifier applies a gain of about 13 dB; and
the combiner is a 3:1 combiner, such that the amplified output signal's power level is about twice the input signal's power level, when losses in the tap, the delay filter, and the combiner are taken into account.
13. The apparatus of claim 11 , wherein the amplifier system is part of an interface unit for a cell site, the interface unit comprising (i) one or more base transceiver station (BTS) ports adapted to be connected to one or more BTSs and (ii) one or more antenna ports adapted to be connected to one or more antennas.
14. The apparatus of claim 13 , wherein the interface unit comprises:
two GSM BTS ports adapted to be connected to a GSM BTS;
two UMTS BTS ports adapted to be connected to a UMTS BTS; and
two antenna ports adapted to be connected to two antennas.
15. The apparatus of claim 14 , wherein the interface unit further comprises a combiner adapted to combine two GSM downlink signals received from the GSM BTS at the two GSM BTS ports to generate a combined GSM downlink signal as the amplifier input signal, where the amplifier system is adapted to amplify the combined GSM downlink signal to generate an amplified combined GSM downlink signal as the amplified output signal.
16. The apparatus of claim 15 , wherein the interface unit is adapted to apply the amplified combined GSM downlink signal to one of the antenna ports for radiation by one of the antennas.
17. The apparatus of claim 13 , wherein the apparatus comprises the interface unit.
18. The apparatus of claim 17 , wherein the apparatus further comprises the one or more BTSs and the one or more antennas.