The power law that governs harmonic distortion states that the second harmonic, when plotted as a function of input power, will have a slope of two on a log scale, and the third harmonic will have a slope of three. This power law is fundamental to the use of intercept points by radio-frequency circuit designers to predict distortion levels from a knowledge of the input signal level. It is shown in this paper that the standard formulation of field effect transistor (FET) models violates this power law for FETs biased at V/sub ds/=0. The problem is shown to arise from discontinuities in the high order derivatives which occur because V/sub gs/and V/sub gd/ are interchanged in the computer models when V/sub ds/ switches sign. A model is presented which does not switch these variables and the new model is shown to follow the correct power law.

The transmission of NTSC composite color images over digital communication channels is generally accomplished by coding the less correlated component signal, YIQ. Unless the video source is available, the component signals are separated from the composite signal by using comb-filters. Comb-filtering is generally performed in the temporal domain. This paper shows that by properly sampling the NTSC composite color signal at four times the color subcarrier, the Walsh-Hadamard transform acts like a comb filter and separates the YIQ components of the composite signal. The YIQ components will be mapped into specific locations of the coefficient matrix.

Predictors operating on video signals sampled at six times the color subcarrier(6f_{c})have been investigated and compared with predictors operating at three times the color subcarrier(3f_{c}). When the best6f_{c}predictor is used with an adaptive delta modulator (ADM) step size generator, the resulting pictures are similar in quality to3f_{c}predictors operating with a four-level adaptive DPCM quantizer. An ADM coder was implemented in real time. The coder used between 24 and 34 IC's, depending upon the algorithm, and fits on a single 9 in × 6 in PC board. The transmission rate is 21.4 Mbits/s.

This paper describes a one-stage look-ahead algorithm for adaptive delta modulators. The algorithm does not require the calculation of two encoding paths nor does it require the decision circuitry to choose the optimum path.

This paper presents the results of a study in data compression of adaptive delta modulated video signals. The Song mode ADM is first investigated at a sampling rate of 16 Mbits/s and shown not to produce enough redundancy to warrant entropy encoding. We then present a modified adaptive delta modulator algorithm that operates at a sampling rate of 16 Mbits/s and does produce sufficient redundancy to yield a 40-50 percent data compression by using a simple code on 4 bit data blocks. Other techniques such as field interpolation and direct substitution are shown to increase the possible data compression further without noticeable degradation in the two input images used in this investigation. The effects of channel errors in the transmission of packet video over a computer network are considered. A leaky integrator is used to reduce the effects of channel errors in the data bits. We show that the effects of channel errors can be reduced by field interpolating those packets that can be shown to contain errors.

This paper describes several adaptive delta modulators designed to meet NASA's potential need to digitally encode video signals. The adaptive delta modulators described are: (1) One-dimensional ADM to encode black-and-white pictures and also transmit digitally encoded voice with no increase in bandwidth (2) An ADM to encode field-sequential color; (3) An ADM to encode color video signals. The units described operate at bit rates that can be adjusted from 6 Mbits/s to 24 Mbits/s. The effects of the bit rate and channel errors on the response of the picture are discussed.

This paper describes several adaptive delta modulators designed to encode video signals. One- and two-dimensional ADM algorithms are discussed and compared. Results are shown for bit rates of 2 bits/pixel, 1 bit/pixel and 0.5 bits/pixel. Pictures showing the difference between the encodeddecoded pictures and the original pictures are presented. Results are also presented to illustrate the effect of channel errors on the reconstructed picture. A two-dimensional ADM using interframe encoding is also presented. This system operates at the rate of 2 bits/pixel and produces excellant quality pictures when there is little motion. We also describe and illustrate the effect of large amounts of motion on the reconstructed picture.

We investigated the effects of channel errors on an adaptive delta modulator used to encode video signals. The investigation revealed that channel errors caused a permanent shift in the dc level of the delta modulator's estimate. Errors in the step size, on the other hand, were transitory and had no noticeable effect on the received pictures. We then presented three error correction schemes to minimize the visibility of the channel errors in the received picture. The first scheme required the transmitter to periodically send the correct dc level of the estimate to the receiver. The second method employed a leaky integrator, and the third method used line-to-line interpolation.