AMPLIFIER DEVICE

There is provided an amplifier device comprising a first directional coupler (12: 30, 32) and a second directional coupler (14: 30′, 32′) connected together so as to create separate upstream (16) and downstream (18) paths in which amplifier means (24, 24′) are located, wherein the first and second directional couplers (12, 14: 30, 32; 30′, 32′) are configured to have different signal loss characteristics, one of the directional couplers having low signal loss characteristics for upstream signals and the other directional coupler having low signal loss characteristics for downstream signals. The signal loss characteristics are preferably the coupling loss of each directional coupler (12, 14: 30, 32; 30′, 32′). The first and second directional couplers may each comprise a microstrip directional coupler (30; 30′) connected to a ferrite directional coupler (50; 50′).

FIELD OF THE INVENTION

This invention relates to an amplifier device for use in cable television and broadband networks.

BACKGROUND TO THE INVENTION

In a broadband network, amplifiers are used to amplify electrical signals from a central network head end down to an individual user (downstream) or from the individual user back to the head end (upstream). In the past the upstream and downstream frequencies were separated in frequency range, the upstream signals using a lower frequency range and the downstream signals using a higher frequency range.

In modern networks, frequency ranges are often altered to give homes an ever faster, greater bandwidth, upstream signal and as such amplifier devices without diplex filters are advantageous so that an expensive upgrade to change the diplex filters is no longer needed when frequency ranges alter.

Amplifier devices without diplex filters use directional couplers instead to create a bi-directional amplifier device. These amplifier devices can incorporate a low-pass filter in an upstream amplifier path to increase isolation above a low-pass frequency. However problems can be encountered with the amount of noise in the upstream signal.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided an amplifier device comprising a first directional coupler and a second directional coupler connected together so as to create separate upstream and downstream paths in which amplifier means are located, wherein the first and second directional couplers are configured to have different signal loss characteristics, one of the directional couplers having low signal loss characteristics for upstream signals and the other directional coupler having low signal loss characteristics for downstream signals.

Thus typically the first directional coupler is configured to have a low signal loss for the signal frequency of the downstream signal and the second directional coupler is configured to have a low signal loss for the signal frequency of the upstream signal, so ensuring the in-to-out coupling of each directional coupler can be optimised. By having different loss characteristics for the first and second directional couplers, the upstream signal has improved signal quality compared to using first and second directional couplers with the same loss characteristics.

Preferably the loss characteristics are coupling loss of the respective directional couplers, so allowing the coupling loss of each directional coupler to be selected dependent on signal frequency Preferably a signal frequency of the upstream signals is different to a signal frequency of the downstream signals.

The first and second directional couplers may each comprise a microstrip directional coupler.

The first and second directional couplers may preferably each comprise a microstrip directional coupler connected to a ferrite directional coupler, thus providing a first directional coupler comprising a first microstrip directional coupler connected to a first ferrite directional coupler and a second directional coupler comprising a second microstrip directional coupler connected to a second ferrite directional coupler. For such an arrangement preferably the first and second directional couplers are arranged such that a coupled port of the first microstrip directional coupler is connected to the second ferrite directional coupler to create the separate downstream signal path. Preferably a coupled port of the second microstrip directional coupler is connected to the first ferrite directional coupler to create the separate upstream signal path.

The or a first amplifier means is preferably located between the coupled port of the first microstrip directional coupler and the output port of the second ferrite directional coupler so as to amplify the downstream signal. The or a second amplifier means is preferably located between the coupled port of the second microstrip directional coupler and the output port of the first ferrite directional coupler so as to amplify the upstream signal.

DESCRIPTION

FIGS.1and2show two versions of an amplifier device10,10′ using two directional couplers to create separate upstream and downstream signal paths in which amplifier elements are located. The amplifier devices10,10′ are bi-directional allowing upstream and downstream signals to pass between the user and a headend associated with the network provider.

InFIG.1, first and second directional couplers12,14are connected together to create separate upstream and downstream signal paths16,18between ports20,22with an amplifier element24,24′ disposed in each signal path. Optional low pass filters26are placed in signal path16either side of amplifier element24.

InFIG.2, the first and second directional couplers each consist of a microstrip directional coupler30,30′ in combination with a ferrite transformer directional coupler32,32′ to create separate upstream and downstream signal paths16,18. Thus first microstrip directional coupler30is connected to first ferrite transformer directional coupler32to create a first directional coupler and second microstrip directional coupler30′ is connected to second ferrite transformer directional coupler32′ to create a second directional coupler.

Each microstrip directional coupler30,30′ consists of an input port40,40′ output port42,42′, coupled port44,44′ and isolation port46,46′. Ferrite directional couplers32,32′ consist of input port50,50′, output port52,52′ and coupled port54,54′.

Coupled port44of microstrip directional coupler30connects to port52′ of ferrite directional coupler32′ to create downstream path18, with amplifier element24′ disposed between ports44and52′. Similarly coupled port44′ of microstrip directional coupler30′ connects to port52of ferrite directional coupler32which is in turn connected to output42of microstrip directional coupler30to create upstream path16in which is disposed amplifier element24. Thus the first and second directional couplers are coupled together to form the separate unidirectional upstream and downstream paths18,16.

The directional couplers12,14,30combined with32,30′ combined with32′, are selected to have different loss characteristics depending on whether they receive an upstream signal for transmission along upstream signal path16or a downstream signal for transmission along downstream signal path18. Typically downstream frequencies are likely to be 1, 1.2, or 1.8 GHz with upstream frequencies typically around 700 MHz. Thus the loss characteristics of first directional coupler12,30combined with32, and in particular the coupled loss characteristics, are configured to be low loss for the highest downstream signal frequency, typically 1, 1.2 or 1.8 GHz, and the loss characteristics of second directional coupler14,30′ combined with32′, and in particular the coupled loss characteristics, are configured to have a low loss for the highest upstream signal frequency, typically 700 MHz.

By having different loss characteristics for the first and second directional couplers, the downstream and upstream signals leaving ports22,20have improved signal quality compared to using first and second directional couplers with the same loss characteristics. The coupled signal loss at directional coupler14,30′ combined with32′ at low frequencies will be lower, thus increasing the upstream signal gain and decreasing the noise figure in the upstream signal path. This is beneficial as a better noise figure improves upstream signal quality greatly. At the same time the in-to-out insertion loss of directional coupler14,30′ combined with32′ will change only minimally in the downstream frequency range and thus will not impair the downstream signal quality.