Showing papers on "Voltage-controlled filter published in 1968"

Optimum Linear Filter for Speech Transmission

Abstract: A common speech‐communications problem is to maximize speech intelligibility over a noisy channel when the transmitter is peak‐power limited. An optimum linear solution is analytically derived, and consists of a speech‐processing filter in the transmitter. The degree of improvement due to use of the filter is derived for a number of bandwidths and signal‐to‐noise ratios. The filter was experimentally verified by articulation tests as the optimum linear configuration, and was significantly more intelligible than other filters that bounded it. Although the optimum filter depends on the noise spectrum, there is no significant difference between it and a noise‐invariant filter for white or speech‐shaped noise. The use of the filter is equivalent to raising the transmitter power between 1 and 10 dB, depending on the speech bandwidth and the signal‐to‐noise ratio.

Adaptive radar clutter rejection

Abstract: A control loop in a radar receiver is jointly responsive to range gated video and a reference potential to establish a filter control signal. A plurality of range gated filters are responsive to the filter control signal to adjust the frequency response in a manner such that clutter is rejected yet the maximum frequency bandwidth is dynamically provided for moving target detection for varying clutter conditions. Each range gated filter has a filter element which is switchable such that the effective electrical properties of the element vary in accordance with the switching to thereby effect a change in the frequency characteristics of the filter. The switching rate is much higher than the pulse repetitive frequency of the radar such that the switching rate does not interfere with signals being processed through the filter. In one embodiment, a variable duty cycle pulse generator having a fixed frequency is utilized to effect control over the frequency characteristics of a filter.

Electromagnetic Interference Reduction Filters

Abstract: This paper presents the theory and application of lumped-image parameter reactive filter networks, absorptive-type filter networks, and combined absorptive-reactive filter networks as conducted electromagnetic interference reduction circuits. A comparison of the passband characteristics by specific examples is given for filter configurations of the pi, T, absorptive, and absorptive-reactive type under implementation conditions of a fixed source impedance and a varying load impedance as encountered when filtering prime power sources feeding ac to dc converters. This paper illustrates the problem the design engineer faces when applying the usual data given in filter catalogs. The filter characteristics are presented for 50-ohm resistive source and load conditions because of MIL-STD-220A quality control testr equirements. A test configuration is recommended to determine the admittance transfer of a filter network, indicative of the networks performance characteristics under application conditions.

An active dual-input RC notch filter

Abstract: The theory and experimental performance of an active RC dual-input notch filter are presented. The frequency of maximum attenuation of the network can be shifted by varying the ratio of the amplitudes of the two input signals without changing the element values of the synthesized network. Comparatively high selectivity around quite low notch frequencies is shown to be realizable.

Practical design of low-frequency bandpass filters

Abstract: THe USEFtJLNESS of bandpass filters for analyzing the EEG frequency spectrum has long been established. The frequency response curves of these filters should have a flat top across the pass band and steep sides to assure maximum attenuation outside the pass band. These requirements can be met by an active filter containhag a number of stagger-tuned, frequency-selective stages, in which each stage consists of a twin-T network connected in the feedback path of an amplifier, qhe twin-T network has been extensively treated in the literature (e.g. HASTINGS, 1946 ; FLEXSHER, 1948 ; COWLES, 1952; BtJCKLrV, 1956, and HYDE, 1957) and fornmlas for stagger-tuning were published by WALLMAN (1948). However, the extent of the calculations, although simple, and the lack of a suitable, easily constructed amplifier circuit have restrained many laboratories from building such filters. This article provides all necessary design data and describes an amplifier circuit developed for purposes of frequency analysis. Bandpass filters with three stagger-tuned stages and five stagger-tuned stages prevail as the most useful in EEG work, where the pass bands of interest are usually of two widths, namely one of approximately 1/4-1/2 octave and one of approximately 3/4-1 octave. Using a stagger-tuned triple for the former and a stagger-tuned quintuple for the latter results in a compromise of adequate rejection outside the pass band and a sufficiently low Q of the individual stages to prevent excessive ringing. In Fig. 1 are shown functional diagrams and typical characteristics of frequency responses. 2. METHOD OF CALCULATION

Low frequency band-pass filter for use in failsafe applications

Abstract: A LOW FREQUENCY BAND-PASS FILTER IS OF A CONSTRUCTION INHERENTLY PROVIDING A SINGLE PREDETERMINED OUTPUT MODE UNDER ANY CONDITIONS OF FAILURE OF ITS INDIVIDUAL COMPONENTS OR COMBINATIONS THEREOF. THE FILTER EMPLOYS COOPERATION BETWEEN THE Q OF A RESONANT CIRCUIT, A RESISTIVE DIVIDER, AND A THRESHOLD CIRCUIT TO DEFINE PASS BANDWIDTH.

A high-performance integrated microwave circuit frequency quadrupler

Abstract: An S - to X -band frequency quadrupler was developed with a 4.0-dB conversion loss and 11-percent bandwidth using hybrid integrated microwave circuit techniques. The multiplier has a low-pass transforming filter on the input and a bandpass filter consisting of half-wavelength lines edge coupled over quarter wavelengths on the output. Design curves for the bandpass filter are given for ceramic microstrip. Two beam-lead varactors were used in the multiplier giving it an input power-handling capability of 3-watts peak power.

Online digital filtering

Abstract: The advantages of the recursive digital filter as a real-time signal processor are stated, and, as an example, a fourth-order Cheby?shev lowpass filter has been synthetised and programmed into an online computer. Typical responses are shown for pulse, step and low-frequency mixed sinusoidal signals.

Use of an undamped galvanometer as low frequency bandpass filter in lock-in amplifiers

Abstract: The use of a galvanometer filter in a low frequency lock-in amplifier is described. The centre of the passband is at a frequency of 035 Hz. The apparatus was tested and it was found that the signal-to-noise ratio was improved by a factor of about 5 over a Keithley 148 nanovoltmeter.

The design of active filters using the in-line pole approximation

Abstract: A synthesis is presented which has enabled a practical switchable filter to be realized which will give an optimum linear phase response together with satisfactory amplitude and transient response using a computed in-line pole distribution. Theoretical and practical characteristics are compared for a fourth- and sixth-order filter and the appropriate circuit diagrams are given. The application of this type of filter is discussed with particular reference to the field of medical electronics.