Radio receiver and gain controlled amplifier therefor

Telecommunications – Receiver or analog modulated signal frequency converter – With particular receiver circuit

Reexamination Certificate

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Details

C455S311000, C455S343200, C330S12400D

Reexamination Certificate

active

06272330

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radio receiver and particularly to a gain controlled amplifier for use in a radio receiver. The radio receiver or gain controlled amplifier may be fabricated from discrete components or as an integrated circuit. In its integrated form, the radio receiver and the gain controlled amplifier can be used in battery powered communications apparatus such as digital pagers and cellular/cordless telephones.
2. Description of the Related Art
For convenience of description the present invention will be described with reference to an integrated receiver for use in a digital pager.
Frequently low power receivers used in applications such as digital paging do not incorporate automatic gain control (AGC). However there are situations, such as when receiving signals in an environment where there are a plurality of very high powered transmitters on nearby channels within the receiver RF bandwidth, that the receiver circuit can be saturated. When the wanted signal amplitude is high enough to allow RF gain reduction AGC provides a means of reducing the received input signal to manageable levels based on the fact that unwanted products caused by large interferers reduce by square or cubic laws, whereas the wanted signal decreases linearly. It is known from European Patent Specification EP-A-0 795 967 to provide AGC to the input stage of a radio receiver to attenuate excessively large input RF signals. This known solution requires a PIN diode which is not readily integratable.
OBJECT AND SUMMARY OF THE INVENTION
An object of the present invention is to provide integratable AGC system in a low power radio receiver.
According to one aspect of the present invention there is provided a receiver comprising means for receiving an input signal, a multi-step gain controlled RF amplifier coupled to said receiving means, means for frequency down-converting the amplified signal, means for measuring the level of a wanted signal, and means for demodulating said signal, characterised in that the multi-step gain controlled amplifier comprises an input terminal, a plurality of N gain stages, where N is an integer of at least 2, having outputs coupled to a common output, a first of the N gain stages being coupled to said input terminal, and an (N−1) stage capacitive ladder attenuator having an input coupled to the input terminal and outputs coupled respectively to an input of each of the second to Nth gain stages, and in that said measuring means has a level control output for switching-on a selected one of the gain stages.
According to a second aspect of the present invention there is provided a gain controlled amplifier comprising an input terminal, a plurality of N gain stages, where N is an integer of at least 2, having outputs coupled to a common output, a first of the N gain stages being coupled to said input terminal, an (N−1) stage capacitive ladder attenuator having an input coupled to the input terminal and outputs coupled respectively to an input of each of the second to Nth gain stages, and switching means responsive to an external signal for switching-on a selected one of the gain stages.
The receiver or amplifier made in accordance with the present invention may be fabricated as an integrated circuit not requiring any external AGC components.
When operating in a gain reduction state, the multi-step, gain controlled amplifier can have a high degree of linearity and low gain but have a low noise, high gain whenever the AGC is not active.
If desired the gains of the gain stages may be identical or they may be different, depending on the application. The attenuation of each of the stages of the capacitive ladder attenuator may be identical or may differ depending on the application.
An advantage of using a capacitive ladder attenuator is that it is essentially a multiband device because although its overall reactance will change with frequency, the relative reactance ratios are maintained.


REFERENCES:
patent: 5561395 (1996-10-01), Melton et al.
patent: 5872481 (1999-02-01), Sevic et al.
patent: 5903854 (1999-05-01), Abe et al.
patent: 5973559 (1999-10-01), Alberty
patent: 5990738 (1999-11-01), Wright et al.
patent: 6054894 (2000-04-01), Wright et al.
patent: 0795967A1 (1997-09-01), None

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