Fast Automatic Gain Control Research Articles

An Improved Digital Automatic Gain Control Method for DAB Receivers

Abstract Digital Audio Broadcasting (DAB) is designed for reliable reception up to vehicle speed of 120 km/h. The high vehicle speed reception requires fast Automatic Gain Control (AGC) to compensate the Rayleigh fading effects in wireless environment. But fast AGC will also incorrectly amplify DAB's null symbol and the following phase reference symbol to cause synchronization problem. Traditional DAB receivers use an 'agc_hold' signal to hold the AGC voltage to avoid the incorrect amplification during the null symbol. But this method requires one extra pin on both the RF tuner and the baseband decoder chips of the DAB receiver. Also it requires good time alignment between the 'agc_hold' signal and the actual null symbol, which brings the complexity to the receiver design. In this paper we proposed an improved AGC method which does not require the 'agc_hold' signal, while still keeps the null symbol quite clear. The new AGC method can be digitally implemented and integrated into the baseband decoder. Comparing to the traditional AGC method, the proposed method reduces the pin numbers of both the RF tuner and the baseband decoder chips. Also it reduces the communications between the RF tuner and the baseband decoder, thus simplifies the receiver design.

Analysis and implementation of digital automatic gain control for DAB baseband decoder

Digital Audio Broadcasting (DAB) receiver requires fast Automatic Gain Control (AGC) to compensate the strength loss due to the multipath propagation in mobile receiving condition. But fast AGC could also incorrectly amplify DAB's null symbol and the following phase reference symbol to cause the synchronization problem. In this paper, we mathematically analyze the AGC circuit under a Rayleigh fading channel and give the basic rule to generate the AGC feedback voltage. Then a fast and high accuracy AGC algorithm with least affection on the DAB null symbol is proposed. The algorithm is simplified to have only add, shift and compare operations, making it easy for hardware and software implementation. Finally the algorithm is simulated and verified on Field Program Gate Array (FPGA) device. The test results show that the proposed AGC algorithm can be settled within 0.5 ms, and keep the received signal stable at a moving speed from stationary to over 120 km/h, both in city and suburban area. The algorithm and the analysis method can also be used for AGC design in other wireless systems.

Real-time range imaging system based on a light-emitting diode array phase-shift range finder for fast three-dimensional shape acquisition

A high-resolution, real-time range imaging system based on a LED array phase-shift range finder was developed to measure three-dimensional surface profiles. The range image is captured by a time-division scanning LED array heterodyne phase-shift range finder. The phase measurement used for obtaining depth is implemented by using the fast "four-bucket" algorithm. The design of a fast automatic gain control circuit obviously reduces the feedback response time and improves system measurement speed. Experimental tests for evaluation of the imaging system performance are described. Based on the theoretical analysis, a simplified signal-to-noise ratio model is proposed for guiding the design of this imaging system. Last, some issues requiring attention on constructing a large-pixel version of the system are also discussed. It was found that the range images can be acquired at a rate of 10 frames per second with a depth resolution better than ±5 mm in the range of 50 to 1000 mm.

Fast Power Transient Management for OC-192 WDM Add/Drop Networks

This paper describes a fast power transient management functionality incorporated into a 12.5 Gb/s maximum likelihood sequence estimation (MLSE) receiver for optical add/drop multiplexer (OADM)-based WDM networks. The receiver has a VGA with a fast automatic gain control and a high-bandwidth offset cancellation loop. Measured results indicate that the receiver IC tolerates a 10 dB/10 mus optical power transient with 72 consecutive identical digits with no BER impact, and offers a 100 X improvement over a standard CDR in tracking an 8 dB sinusoidal power transient at a BER of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> .

Fast Burst Synchronization for Power Line Communication Systems

Fast burst synchronization is an important requirement in asynchronous communication networks, where devices transmit short data packets in an unscheduled fashion. Such a synchronization is typically achieved by means of a preamble sent in front of the data packet. In this paper, we study fast burst synchronization for power line communication (PLC) systems operating below 500 kHz and transmitting data rates of up to about 500 kbps as it is typical in various PLC network applications. In particular, we are concerned with the receiver processing of the preamble signal and the actual design of preambles suitable for fast burst synchronization in such PLC systems. Our approach is comprehensive in that it takes into account the most distinctive characteristics of the power line channel, which are multipath propagation, highly varying path loss, and disturbance by impulse noise, as well as important practical constraints, especially the need for spectral shaping of the preamble signal and fast adjustment of the automatic gain control (AGC). In fact, we regard the explicit incorporation of these various requirements into the preamble design as the main contribution of this work. We devise an optimization criterion and a stochastic algorithm to search for suitable preamble sequences. A comprehensive performance comparison of a designed and two conventional preambles shows that the designed sequence is superior in terms of (a) fast burst synchronization in various transmission environments, (b) fast AGC adjustment, and (c) compliance of its spectrum with the spectral mask applied to the data transmit signal.

1.25 Gbit/s ITU-T G.984.2 burst-mode transimpedance amplifier without reset pins

A DC-coupled burst-mode transimpedance amplifier including fast automatic gain control is presented. By employing common-mode level signalling, a reset signal is provided without adding additional package pins. This transimpedance amplifier can be used in the upstream part of ITU-T G.984.2 compliant passive optical networks.

Aircraft scintillation spectra

Using the model of aircraft reflection developed by DeLano, the spectra of the reflection signals are found. Spectra for the amplitude of the rectified return, for the angular fluctuation signal associated with a fixed radar line-of-sight (effective radar center fluctuation), and for the angular fluctuation signal associated with a zero time constant servo (apparent radar center fluctuation) are derived. Several types of target motion are considered: uniform rotation, random rotation, and rectilinear velocity toward the radar itself. Each of these motions produces a characteristic spectrum and the properties of these spectra are pointed out and their significance in radar system design emphasized. In particular, the importance of the spectral density at zero frequency of the apparent radar center is shown in relation to systems using very rapid automatic gain control (AGC). It is shown that such use of very fast AGC may increase this noise density by a factor of approximately three, and thus increase the system noise.