Home electric power distribution wiring is used for delivering electric current to home appliances. This power distribution network can also be used to transmit signals to provide communications between analog or digital devices. It has been recognized for some time that there are distinct advantages to using power distribution networks for networking computerized devices, but there are very few interfaces available for connecting devices to power distribution networks. It is also well known that power distribution networks are subject to high levels of electrical noise, and that noise affects the quality of signal transmission. Power distribution networking therefore requires interfaces with receivers that have extended capability for extracting useful signals from the wide spectrum of signals present on the electrical wiring of a home power distribution network.
A multi-carrier technique referred to as orthogonal frequency division multiplexing (OFDM) is widely used for power distribution networking, because this technique is robust and permits multi-path propagation. The OFDM technique, which is well known in the art, includes a transmitter and a receiver. The receiver normally has an amplifier with automatic gain control (AGC). The function of the AGC is to adjust an amplitude of an input signal to match an amplitude range of an analog-to-digital converter (ADC) to inhibit signal clipping by the ADC. The characteristics of AGC governs the quality of some aspects of the communications receiver.
Many methods for AGC are taught in the prior art, they are used in audio, video, radio, digital radio, cellular phones, etc. The main purpose of AGC is to adjust the amplitude of the incoming signal so that it matches a preferred operating range of the ADC and to produce a high quality output signal.
U.S. Pat. No. 6,122,331 issued to Dumas on Sep. 19, 2000 and is entitled “Digital Automatic Gain Control”. Dumas describes a complicated AGC that includes a gain correction unit that is responsive to attenuate and amplify commands issued from a feedback system that monitors the output of the AGC. The feedback system not only detects when gain changes are required, but also determines an optimal time at which the gain should be changed. The AGC also includes a transition region detector which responds to an increase or decrease communicated in a gain control command. If the magnitude of the input signal is greater than a predetermined value, then the transition region detector places a disable signal on its control output to prevent the gain correction unit from altering the gain. A disadvantage of this system is its complexity.
The principal problem that must be considered when designing an AGC is that, in terms of cost/complexity, the trade off between sampling rate and dynamic range of the A/D converter must be considered. In Power distribution networking, receivers must accommodate a large analog input dynamic range, and a large digital output dynamic range. However, affordable A/D converters have a limited dynamic range at normal sampling rates.
There therefore remains a need for a low-cost digital signal gain control circuit that is relatively simple, and seamlessly integrates the A/D converter into the receiver to provide an accurate absolute measurement of the incoming signal amplitude to enable an output signal of high quality.