Amplifier circuit, integrated circuit and radio frequency communication unit

Abstract

An amplifier circuit for amplifying an input signal received at an input node of the amplifier circuit. The amplifier circuit comprises a feedback resistance connected between the input node of the amplifier circuit and an output node of the amplifier circuit. Transconductance circuitry is arranged to inject a transconductance current at a point along the feedback resistance. The transconductance circuitry is configurable to vary the point along the feedback resistance where the transconductance current is injected.

Description

FIELD OF THE INVENTION[0001]The field of this invention relates to an amplifier circuit, an integrated circuit and a radio frequency communication unit comprising such an amplifier circuit and / or integrated circuit. The invention is particularly applicable to, but not limited to, a variable gain low noise amplifier circuit.BACKGROUND OF THE INVENTION[0002]In the field of radio frequency (RF) communication receivers, the main task of the receiver front-end circuit is to process a signal that is received by an antenna coupled to the receiver front-end circuit in such a manner that it can be more easily processed by subsequent receiver circuits, for example, demodulation circuitry. Typically, such front-end circuits comprise low noise amplifier (LNA) circuitry for amplifying the received RF signal, and mixer circuitry arranged to perform frequency translation of the amplified radio frequency signal to a lower intermediate or baseband frequency. The intermediate / baseband frequency signa...

AI Technical Summary

Benefits of technology

This approach enables reduced power consumption in low gain configurations, improved noise performance, and scalability without the need for on-chip analogue components like inductors, while maintaining constant input impedance and achieving efficient variable gain amplification.

Problems solved by technology

However, due to the high operating frequencies and the low signal levels of the received RF signal, only a very limited number of circuit techniques may be used to successfully implement the front-end circuitry that comprises the LNA circuitry and the mixer circuitry.

The primary challenge in the design of an LNA circuit is to minimise noise.

A problem with this approach is that it is inefficient in terms of current consumption, particularly at low gain settings.

Since the input impedance of the amplifier topology 100 at resonance is real, and is proportional to the transconductance of transistor M1110, such a current reduction would result in a change in the input impedance of the amplifier, which would cause a mismatch with, for example, an antenna coupled thereto.

A further problem with the amplifier topology 100 of FIG. 1 is that it exhibits a poor linearity performance.

Whilst this may be beneficial in terms of noise, it also increases the distortion introduced by transistor M1110.

A problem with a traditional common-gate amplifier topology is that the theoretical best noise figure (NF) achievable is limited to 2.2 dB.

The achievable noise figure is limited by the fact that the transconductance of the input device not only defines the noise characteristic of the amplifier, but it also determines its input impedance.

However, the noise performance of such an amplifier topology 200 of FIG. 2 is still unable to match that of the inductively degenerated amplifier topology 100 of FIG. 1.

However, this configuration is not popular for the implementation of highly integrated receivers for mobile applications for two main reasons.

Firstly, for proper operation the transconductance of transistor M1310 has to be quite large (>100 mS), resulting in the amplifier, and in particular implementations comprising MOSFETs, being power hungry.

Secondly, no straightforward way of implementing various gain settings has been proposed, as both the gain and the input impedance of the amplifier are functions of the feedback resistor RF 320, of the load resistor RL 330 and of the transconductance of M1 in a non-trivial way.

In addition to the above identified short comings of the prior art topologies, analogue circuits comprising components, such as inductors, are unable to scale and provide comparable improvements in integrated circuit manufacturing processes in the same manner as digital circuits.

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