A LOW NOISE AMPLIFIER FOR AN ELECTRICALLY SMALL ANTENNA

FIELD OF INVENTION

The present invention relates generally to low noise amplifiers, and particularly to a low noise amplifier (LNA) for an electrically small antenna.

BACKGROUND

A current trend for portable radio communication devices, such as mobile phones, PDA, portable computers and similar devices, is to provide the device with a DVB-H (Digital Video Broadcasting: Handhelds) receiver. This is in addition to other components for which the available space of the device is already limited.

One way of minimizing use of the space of a device is to use an electrically small antenna, which however reduces the quality of signals received at a DVB-H receiver. An electrically small antenna has an electrical size which is much smaller than wavelength corresponding to its intended resonance frequency/frequencies.

SUMMARY OF THE INVENTION

An object of the present invention is to improve the quality of signals received at a broadband radio receiver such as a DVB-H receiver.

This object, among others, is according to the present invention attained by a low noise amplifier arrangement, an antenna arrangement, a broadband radio receiver arrangement, a portable radio communication device, and a method for processing broadband radio signals, respectively, as defined by the appended claims .

By providing impedance matching and gain equalization of the broadband radio signals amplified by an LNA the quality of signals is improved, despite lowered gain of the combined LNA and equalizer, since saturation of a broadband radio receiver is avoided.

The invention is primarily, but not exclusively, aimed for DVB-H technology.

Further features and advantages of the present invention will be evident from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description of embodiments given below and the accompanying figures, which are given by way of illustration only, and thus, are not limitative of the present invention, wherein:

Fig. 1 schematically shows the receiving parts of a portable radio communication device up to a DVB-H receiver arrangement;

Fig. 2 schematically shows a radio frequency equivalent scheme for an electrically small antenna and a low noise amplifier having a grounded input transistor;

Fig. 3 schematically shows a low noise amplifier arrangement comprising a low noise amplifier and an equalizer;

Fig. 4 schematically shows a series equalizer between a DVB-H receiver and a low noise amplifier;

Fig. 5 schematically shows a parallel equalizer between a DVB-H receiver and a low noise amplifier; and

Fig. 6 schematically shows a parallel and a series equalizer between a DVB-H receiver and a low noise amplifier.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following description, for purpose of explanation and not limitation, specific details are set forth, such as particular techniques and applications in order to provide a thorough understanding of the present invention. However, it will be apparent for a person skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed description of well-known methods and apparatuses are omitted so as not to obscure the description of the present invention with unnecessary details.

Only the components and functions up to the DVB-H receiver will be discussed in connection with the present invention, since other processing to a DVB-H signal is independent of that of the present invention.

A preferred embodiment of the present invention will now be described with reference to Figs. 1-6.

A low noise amplifier arrangement 2 is provided between a

DVB-H receiver 3 and an electrically small antenna 1, which is illustrated in Fig. 1. The low noise amplifier arrangement 2 is arranged to amplify DVB-H signals received from the electrically small antenna before they are received in the DVB-H receiver, in a portable radio communication device, such as a mobile phone, a computer or similar devices .

The electrically small antenna 1 is preferably tuned to the desired DVB-H frequencies together with the low noise amplifier arrangement 2. The low noise amplifier arrangement

2 in such a case has an input transistor connected to ground. At a resonance frequency the electrically small antenna 1 and the input transistor of the low noise amplifier arrangement 2 can be modeled by an equivalent scheme, which is illustrated in Fig. 2. The model comprises the electrically small antenna 1 modeled as a signal generator 4 followed by a capacitor 5 in series with an inductor 6. The model also comprises the input transistor of the low noise amplifier arrangement 2 modeled as a capacitor 8. Residual resistance is modeled by the resistor 7 in series between the inductor 6, which also can be an external lumped component, and the capacitor 8. The signal output from the low noise amplifier arrangement 2 is taken from point 9 of the model. In this way the electrically small antenna 1, together with the input of the low noise amplifier arrangement 2, can be tuned to λ/4 of the desired DVB-H frequencies when a ground plane is used, or can be tuned to λ/2 of the desired DVB-H frequencies when no ground plane is used, and will thus occupy less space in the portable radio communication device compared to an electrically large antenna.

The low noise amplifier arrangement 2 comprises an LNA 10 at the input of the low noise amplifier arrangement 2 and an equalizer at the output of the low noise amplifier arrangement 2, which is illustrated in Fig. 3. The equalizer can e.g. be a series passive equalizer 11, which is illustrated in Fig. 4, a parallel passive equalizer 12, which is illustrated in Fig. 5, or an active equalizer (not illustrated) .

A series passive equalizer 11 comprises a combination of passive components equal to a capacitor, an inductor, and a resistor in parallel, which are provided in between the low

noise amplifier 10 and the DVB-H receiver 3. A parallel passive equalizer 12 comprises a combination of passive components equal to a capacitor, an inductor, and a resistor in series, which are provided between the low noise amplifier 10, the DVB-H receiver 3 and ground. An active equalizer comprises a plurality of component comprising transistors or similar, also provided between the low noise amplifier 10 and the DVB-H receiver 3. The equalizer can also easily be made of a combination of a series and a parallel passive equalizer, which is illustrated in Fig. 6. In addition to equalizer components can matching resistor be added, wherein a series matching resistor is used for a parallel equalizer, a parallel matching resistor is used for a series equalizer, and both a parallel and a series matching resistor is used for a combination of a series and a parallel passive equalizer.

A common low noise amplifier for DVB-H signals has a gain G of about 18 dB, and a gain variation δG of about 18 dB. By- providing the low noise amplifier arrangement 2 with such a low noise amplifier followed by an equalizer a low noise amplifier arrangement with low δG is provided, and saturation of the DVB-H receiver 3 is avoided. By avoiding saturation of the DVB-H receiver 3 the quality of the signals is improved, and thus images displayed based on such signals also get improved quality. The low noise amplifier arrangement 2 has a gain variation δG of at most 6 dB, preferably at most 3 dB to avoid saturation of the DVB-H receiver. The low noise amplifier arrangement 2 will only get a gain G of at most 3 dB, preferably at most 0 dB, but the quality of the DVB-H signals are nevertheless improved.

The low noise amplifier arrangement 2 is further impedance matched to the subsequent DVB-H receiver 3. The impedance

matching between the low noise amplifier arrangement 2 and the DVB-H, receiver 3 is usually selected to 50 ω, but could have other common impedances . The output impedance of the low noise amplifier arrangement 2, matching the input impedance of the DVB-H receiver 3, is provided by the equalizer, preferably by adding a resistor at its output, either as a series resistor or as a parallel resistor. This will provide an optimal noise figure (NF) in the DVB-H receiver 3 and the best input filter performance of the DVB-H receiver 3.

An antenna arrangement can be provided comprising the electrically small antenna 1 and the low noise amplifier arrangement 2. Alternatively, a DVB-H receiver arrangement can be provided comprising the DVB-H receiver 3 and the low noise amplifier arrangement 2. Also, a portable radio communication device, such as a mobile phone, computer or similar devices, can be provided comprising a DVB-H receiver 3, an electrically small antenna 1, and a low noise amplifier arrangement 2 , wherein the low noise amplifier arrangement 2 can be provided as a separate unit, combined with the electrically small antenna 1, combined with the DVB-H receiver, or all three parts combined together.

A DVB-H signal is thus processed in the following way in a portable radio communication device. Firstly, DVB-H signals are received in an electrically small antenna. Thereafter, the received DVB-H signals are low noise amplified, the amplified signals are equalized and impedance matched, comprising impedance matching of the amplified signals to the subsequent DVB-H receiver and equalizing the gain variation of the amplified signals to at most 6 dB. Thereafter, the equalized and impedance matched signals are received in the subsequent DVB-H receiver.

While the above embodiments have been disclosed in conjunction with DVB-H technology, the invention is not limited to this technology. The invention can be employed for any kind of broadband radio or digital video technology for portable radio communication devices using electrically small antennas .

It will be obvious that the present invention may be varied in a plurality of ways. Such variations are not to be regarded as departure from the scope of the present invention as defined by the appended claims. All such variations as would be obvious for a person skilled in the art are intended to be included within the scope of the present invention as defined by the appended claims.