Adjustment of amplitude and DC offsets in a digital receiver

Abstract

A nonlinear adaptive mechanism for amplitude adjustment and DC estimation and compensation for use in a digital receiver such as a Bluetooth GFSK receiver. The mechanism uses a feed-forward technique that can be used in a multi-stage scheme to perform both DC compensation and amplitude adjustment of an input signal for use by subsequent processing stages. In a first stage, coarse DC offset compensation is performed and the offset estimates generated are subsequently frozen. In a second stage, the incoming signal with the DC offset subtracted from it, is then scaled into a narrow predefined range of amplitudes using a scaling mechanism that works with gains and attenuations that are powers of two in order to simplify implementation. In a third stage, the scaled compensated signal is then injected again into the same DC estimation mechanism, which was previously used for DC compensation in the first stage, for further DC offset estimation and compensation (i.e. fine DC estimation and compensation).

Description

FIELD OF THE INVENTION [0001] The present invention relates to the field of data communications and more particularly relates to a method of and apparatus for adjustment of amplitude and DC offsets in a digital receiver. BACKGROUND OF THE INVENTION [0002] In digital communications systems, a carrier signal is modulated with the digital data to be transmitted over the channel, where it typically suffers various forms of distortion, such as additive noise. The digital data is often transmitted in bursts wherein each burst consists of a number of data bits. Upon reception, the signal must be demodulated in order to recover the transmitted data. [0003] It is common for receivers to employ direct conversion (i.e. homodyne receiver) to perform the demodulation of the received signal. The received signal is mixed with a~local oscillator signal at the carrier frequency to produce I (in-phase) and Q (quadrature) baseband signals. An advantage of direct conversion receivers is that they are e...

AI Technical Summary

Benefits of technology

The present invention provides a mechanism for amplitude adjustment and DC offset compensation in a non-linear adaptive manner. The mechanism can be used in a multi-stage digital scheme to perform both DC compensation and amplitude adjustment of an input signal for use by subsequent processing stages. The DC compensation mechanism is relatively small in size and adapts quickly to changing DC levels. The non-linear nature of the mechanism allows for fine DC offset cancellation even at low IF levels. The DC compensation mechanism can be implemented in a relatively small size and adapts quickly to changing DC levels. The invention provides a method and apparatus for DC offset compensation that can be used in embedded devices and can achieve performance degradation in prior art solutions. The invention also provides a method and apparatus for amplitude adjustment and DC offset compensation that can be used in a multi-stage digital scheme to perform both DC compensation and amplitude adjustment of an input signal for use by subsequent processing stages.

Problems solved by technology

This is in contrast to prior art solutions where filtering distorts the signal's spectrum and causes performance degradation.

For example, suppressing DC which is 100 dB above the level of the received signal and is very close to it in frequency (IF of 500 kHz) is almost impossible using linear filtering.

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