DOI:10.1049/ree.1978.0024

出版商:IERE    

年代:1978

数据来源: IET

摘要:

The paper describes an Adaptive Delta Modulation (ADM) system which has been developed to operate at bit rates of 9.6 kbit/s and lower. The step size is adapted by deriving a control signal from the output bit stream and modifying the feedback signal in the second loop of a two-loop ADM coder through an f.e.t. multiplier. The system has an s.n.r. of 16 dB or more over an input range of 20 dB for a sinusoidal input of 400 Hz at the bit rate of 9.6 kbit/s. Extensive subjective tests of speech processed at 9.6 and 7.2 kbit/s have been carried out using the category judgement method and the modified rhyme test. At 9.6 kbit/s a mean intelligibility score of 88% and at 7.2 kbit/s a score of 74% have been obtained.

DOI:10.1049/ree.1978.0025

出版商:IERE    

年代:1978

数据来源: IET

摘要:

A tracking correlation receiver being developed as part of a flux-density measurement programme for 12·5 MHz radio sources will employ three type-one negative feedback loops. An amplitude insensitive phase loop will control an internal phase shifter to track radio sources through an interferometer aerial pattern. Simultaneously, this loop will keep the inputs to an amplitude multiplier in phase or antiphase. Relative phase read-out will provide for detection of possible phase scintillation.An amplitude loop will use the integrated output from an amplitude multiplier to control a variable reference noise source whose output is added directly to the aerial inputs. This loop will keep the time-averaged multiplier output nulled, such that the output level setting of the controlled reference source is, at all times, indicative of the signal power received by the aerials.A third loop will control an independent noise source whose output is added to one receiver channel. This loop will provide an output of the total noise power received and will keep the operating points of all receiver elements equal in the two channels. The proposed receiver combines principles developed by the authors with those of several other workers. The overall receiver scheme is expected to provide exceptional accuracy and stability, independent of channel gain, phase, and bandwidth. Frequent recalibration will be unnecessary. This paper describes the operation of the proposed receiver scheme and provides test results and data regarding an analogue simulation study of the multiple feedback loop schemes to be used in the receiver.

DOI:10.1049/ree.1978.0026

出版商:IERE    

年代:1978

数据来源: IET

摘要:

The generally adopted design philosophy of interconnections between digital circuits considers it safe to use unmatched lines for short distances, and matched lines for long distances. These terms long and short are not usually meaningfully quantified. With higher-speed digital logic this philosophy has often degenerated into a ‘match every interconnection for safety’ concept, with consequential increases in can count, complexity, down-time, volume and power consumption, leading to a degradation of overall system speed.This paper investigates the propagation of pulses down interconnections to discover the point where the matching of lines becomes essential. Bergeron diagrams are used in a theoretical analysis to predict the waveforms that will be generated by various lengths of interconnection; these results are subsequently compared with actual measurements on emitter-coupled logic working under similar conditions.

DOI:10.1049/ree.1978.0027

出版商:IERE    

年代:1978

数据来源: IET

摘要:

A two-bit instantaneously adaptive delta modulator intended for application as the input stage of a code converter is presented. Its step adaptation algorithm is derived from that used in high information delta modulation (HIDM). The improvement in performance relative to the HIDM system is gained by its ability to reduce overshoots and respond faster to signal variations. A hardware model that allows the comparison between these delta modulators is described and results of measurements on narrow-band noise and sinewave input signals are presented. Two possible structures to generate p.c.m. signals by code conversion are described and computer simulation results presented for one of them.

DOI:10.1049/ree.1978.0028

出版商:IERE    

年代:1978

数据来源: IET