Order Low Pass Filter Research Articles

Reducing nonlinear waveform distortion in IM/DD systems by optimized receiver filtering

Nonlinear waveform distortion caused by the combined effect of fiber chromatic dispersion, self-phase modulation, and amplifier noise limits the attainable performance of high bit-rate, long haul optically repeatered systems. Signal processing in the receiver is investigated and found to be effective in reducing the penalty caused by this distortion. Third order low pass filters, with and without a tapped delay line equalizer are considered. The pole locations or the tap weights are optimized with respect to a minimum bit error rate criterion which accommodates distortion, pattern effects, decision time, threshold setting and noise contributions. The combination of a third order Butterworth filter and a five-tap, fractionally spaced equalizer offers more than 4 dB benefit at 4000 km compared with conventional signal processing designs.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Frequency response of mature guinea-pig outer hair cells to stereociliary displacement

Outer hair cells (OHC) were isolated from the apical two turns of the guinea-pig cochlea and their hair-bundle stimulated mechanically by a glass probe. In accordance with in vivo data ( Dallos, 1985), the resting membrane potential was typically −64 mV ( N = 200). The maximum amplitudes of the receptor potentials were between 0.4 and 5.2 mV peak-to-peak, with mean of 1.5 mV ± 0.9 mV ( N = 81). The sensitivity was 0.015 mV/nm or 2 mV/deg. The frequency response of the receptor potential followed a first order low-pass filter characteristic with a corner frequency of about 63 Hz. For frequencies up to at least 1.6 kHz, the frequency response of mechanoelectrical transduction was dominated by the electrical input impedance of the cell. The presence of a single time constant in the voltage response to stereociliary deflection implies that the frequency response of mechanoelectrical transduction far exceeds that of the electrical input impedance of the cell; its time constant must be faster than 100 μs. Under in vivo conditions, OHC should be capable of providing a sufficiently large receptor potential to supply enough energy for electromechanical feedback.

Pulse modulation detection in human motion vision

We present data on the human sensitivity to temporal pulse modulations of target velocity. We measured threshold detection modulation amplitudes for pulse-shaped speed modulations, as a function of pulse duration and temporal frequency. At short pulse durations (up to 50 msec) and low modulation frequency (1 Hz), detection amplitudes are ruled by Bloch's law: the product of pulse duration and threshold modulation amplitude is a constant. This constant corresponds to a position modulation with an amplitude of 3 arc min in a coordinate frame that moves at the average speed (3deg/sec) of the target. At longer pulse durations we find deviations from Bloch's law. Speed modulation thresholds are not critically dependent on target luminance contrast. These results are modeled by a modulation detection process in two stages. A functional description of the first stage is filtering of the true speed modulation signal by a second order low-pass filter with a characteristic time constant of 20–25 msec. The second (decision) stage is variance detection: modulations are detected when the variance of the filtered modulation function exceeds a certain threshold variance. The square-root threshold variance is estimated 8–10%. This two-parameter model accurately predicts the measured dependence of pulse modulation detection thresholds on pulse duration and pulse density.

A theoretical and experimental investigation of explicit force control strategies for manipulators

This paper presents a complete overview of basic strategies that have been proposed for force control of robot manipulators. First, the model of the plant to be controlled is reviewed. Next, the strategies are divided into force-based and position-based categories, according to previously reported implementations. Each of the controller types within these categories is analyzed, and predictions of stability and efficacy are made. Then it is shown that these two categories are actually the same, and this recognition leads to the concept of a novel second order low pass filter controller. Finally, all of the controllers are experimentally tested on the CMU DD Arm II, confirming the theoretical predictions. Among the important results presented is the conclusive demonstration for the first time that integral gain control is the best basic strategy for force control of manipulators.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Visual processing of optic acceleration

We present data on the human sensitivity to optic acceleration i.e. temporal modulations of the speed and direction of moving objects. Modulation thresholds are measured as a function of modulation frequency and speed for different periodical velocity vector modulation functions using a localized target. Evidence is presented that human detection of velocity vector modulations is not directly based on the acceleration signal (the temporal derivative of the velocity vector modulation). Instead, modulation detection is accurately described by a two-stage model: a low-pass temporal filter transformation of the true velocity vector modulation followed by a variance detection stage. A functional description of the first stage is a second order low-pass temporal filter having a characteristic time constant of 40 msec. In effect, the temporal low-pass filter is an integration of the velocity vector modulation within a temporal window of 100–140 msec. A non-trivial link of this low-pass filter stage to the temporal characteristics of standard motion detection mechanisms will be discussed. Velocity vector modulations are detected in the second-stage, whenever the variance of the filtered velocity vector exceeds a certain threshold variance in either the speed or direction dimension. The threshold standard deviations for this variance detection stage are estimated to be 17% for speed modulations and 9% for motion direction modulations.

Biomechanics of a muscular hydrostat: a model of lapping by a reptilian tongue

We have developed a quantitative model of an example of a muscular hydrostat, a reptilian tongue, and have used this model to study a functional movement, protrusion and retrusion, a form of lapping. The model tongue consists of a longitudinal muscle that shortens the tongue when it contracts, and a circumferential muscle wrapped around the longitudinal muscle that lengthens the tongue when it contracts. The anatomy of the model tongue and the pattern of activation of its muscles are based on studies of the tongue of the lizard Tupinambis nigropunctatus (Smith 1984). The mechanics of pressure vessels were used to derive a relationship between the forces in the two muscles. Muscle force production was modelled as the product of length/tension properties, force/velocity properties, and activation due to neural inputs (incorporating both recruitment and firing period). Passive forces were modeled as a force in parallel with the longitudinal muscle. Muscle activation dynamics were modeled as a first order low pass filter. When the model tongue is short, the two muscles can lengthen or shorten it with comparable forces, but as it lengthens, the force that the circumferential muscle can exert drops precipitously. When the tongue is long, it can neither be very stiff, nor can it generate much force. The model also reproduces the kinematics of lapping movements actually observed in Tupinambis.

Switched current filters

‘Switched Currents’ is a new analogue sampled-data signal processing technique that can be implemented without the need for linear floating capacitors. This feature enables signal processors to be integrated in a standard digital VLSI process (CMOS), making the technique ideally suited for mixed analogue/digital ICs. Switched current cells are described, and a configuration for a universal integrator is developed that is exactly equivalent to a switched capacitor counterpart. With this integrator, complete switched current filters may be constructed from switched capacitor prototypes. This demonstrated by the ‘exact’ design and simulation of a sixth order lowpass filter with a cutoff frequency of 5MHz.

Non-rigid response of the trunk to dynamic axial loading: an evaluation of current modelling assumptions

Most biomechanical models of the trunk and limb system represent the segments as rigid links joined with pins. The implication of this simplifying assumption is that dynamic loads applied to the body are instantaneously transmitted through the linkage with no distortion of the applied force-time waveform. The purpose of this study was to determine whether this assumption was justifiable for loads applied to the hands or shoulders and transmitted through the trunk to the bottom of the pelvis. If not, the intent was to find a transfer function relating load inputs applied to the top of the trunk and outputs measured at the bottom of the trunk. Loads were manually applied to a force transducer attached to a shoulder yoke or to a hand-held loading pan mounted on three subjects. The subjects sat both erect and slouched and also varied the trunk stiffness by voluntarily changing trunk muscle activation. Subjects sat on a rigid steel stool mounted on a force plate from which force outputs were recorded. In addition, a few case studies were performed; some trials utilized light impacts by a hammer to the transducer mounted on the crown of the bare head and in other trials the body was in a standing (lifting) posture. The results indicated that the mechanical response is indeed time dependent. For applied forces with a rise time less than 20 ms (hammer impact) the trunk system reduced the magnitude of the force peaks by up to 40%. However, for applied loads with rise times from about 30 to 300 ms the peak output force was larger than the applied force peak. This was due to inertial effects of the upper body mass as it ‘rebounded’ from the applied load. During these conditions of biologically generated applied forces, the output could be reasonably reconstructed by processing the input signal through a Butterworth second order low pass filter with a cutoff frequency of 7·5 Hz, a gain and in some cases, a shift in time up to 20 ms. The assumption of rigid body segments in these experiments appeared reasonably justified when the rise time of the applied force was greater than approximately 300 ms. However, for input signals that had a shorter rise time the trunk did not behave rigidly.

Prey attack in crayfish: conditions for success and kinematics of body motion

1. An experimentally blinded crayfish (Cherax destructor) attacks an object that briefly touches the flagellum of its second antenna. Since there is no feedback control during the attack, the entire motor command has to be preprogrammed immediately after stimulation. 2. I studied the dynamics of the attacks by video film analysis and by decomposing the motion of the body into rotation around a centre on the long axis of the body and a translation parallel to it. The time course of both rotation and translation velocities can be fitted by pulse responses of third order low pass filters. 3. It is shown that the model of Zeil et al. (1985) to describe the attacks is adequate only, when the distancedA of the point of stimulation from the base of the antenna is short. For longer distances it predicts an insufficient rotation, and a translation larger than required. The discrepancy is traced back to the fact that crayfish simultaneously translate and rotate during an attack. 4. To program a successful attack the crayfish have the option to adjust the extent of rotationaw and that of the translationav, as well as the ratio of their time constants. They fit bothaw andav todA but do not vary the time constants. 5. It is demonstrated that for the purpose of motion analysis a centre of rotation and a translation velocity component orthogonal to the body long axis cannot be derived unequivocally. One of them has to be chosen arbitrarily. 6. The peculiarities of the crayfish' attack as compared with prey catching strategies in other animals, and the limits of single frame analysis regarding conclusions about neural events are discussed.

The contractile properties and movement dynamics of pigeon eye muscle.

The lateral rectus (LR) muscle of the pigeon was directly stimulated in situ at 41 degrees C. The length tension relationships for active and passive tension were investigated to determine the optimum muscle length (Lo). Isometric responses to single and twin pulses, tetani and sinusoidal stimulation were measured. A linear relationship was found between length and active tension during stimulation. Increase in stimulation frequency produced a corresponding shift in tension with the slope of the curves remaining the same. At Lo (1.21 times resting length) the average contraction time of single twitches was 6.03 ms and the half-relaxation time was 7.77 ms. Stimulation frequencies of 200 Hz and over gave rise to a fused tetanus. Tension increased to a maximum at 200 Hz and rate of tension rise saturated at 600 Hz. The tension response to tetanic stimulation was linear over the range 70-180 Hz. Maximum tetanic tension was around 3.48 N/cm2 and the twitch:tetanus ratio was 0.164. Prolonged activation at fusion frequency showed a high fatigue resistance. Sinusoidal stimulation with pulse trains of 100-180 Hz produced a sinusoidal response over the frequency range 0.6-40 Hz, from which the gain and phase relationships were determined. The muscle response approximates a first order low pass filter, with a characteristic frequency of 11.2 Hz. There is an additional phase lag, equivalent to the response latency, of 2.89 ms. The results are compared to the contractile properties of mammalian eye and avian skeletal muscle. The frequency response of the LR is compared to that of cat soleus and gastrocnemius and to pigeon eye movement dynamics.

A stray-insensitive single switched-capacitor ladder realization of an arbitrary order low-pass filter

A stray-insensitive biphase SC realization of an all-pole filter of any desired order is first obtained in the ladder form with all the SCs of equal value. These equal-valued SCs are then replaced by a single time-shared SC. Like any other time-multiplexed circuit, this circuit also requires an increased number of clock phases. Thus against an increase in the die area to generate a multiphase clock on the chip, there is a saving due to the reduction in the total capacitance. One such fifth-order low-pass filter is designed and tested with discrete components to verify its performance.

Elasmobranch eye motor dynamics characterised using pseudorandom stimulus.

A pseudorandom binary sequence electrical pulse rate stimulus was delivered to the abducens nerve of an elasmobranch preparation. Ipsilateral eye movements were recorded using a position-sensitive photodiode to measure the position of a reflective patch attached to the fish's eye. Eye position data was cross-correlated with the stimulus pattern, and exponential decay curves were fitted to the cross-correlograms to estimate the time constant of a linear first order low-pass filter model. The cross-correlograms were transformed into the frequency domain using a Digital Fourier Transform, and Bode plots of eye dynamics were plotted. Eye motor plant dynamics in the elasmobranch Cephaloscyllium isabella can be accurately characterised by a linear first order low-pass filter model with a corner frequency of 0.73 +/- 0.10 Hz. Non-minimum phase lag reaches 90 degrees at about 4 Hz, indicating a time delay of some 50-60 ms. Integration of the canal signal is not required for producing compensatory eye movements above the characteristic frequency of the eye motor plant. However, the canal signal may be integrated to ensure that the vestibulo-ocular reflex is compensatory at lower frequencies. Substantial phase compensation or prediction is required for effective control of the vestibulo-ocular reflex.

A class of low-noise computationally efficient recursive digital filters with applications to sampling rate alterations

A new structure for multiband recursive digital filters is proposed. For meeting low-pass filter specifications, it uses fewer multiplications than conventional elliptic filter realizations. An approximation to the minimax solution is obtained numerically by minimizing the LP error norm. The analytic optimum for odd order low-pass filters of this new class turns out to be the elliptic filter itself, but in a new configuration. Analytic solution is also obtained for filters used in decimation/interpolation by a factor of 2. There are several realizations for this new structure, the choice of which depends on the location of poles and zeros. Some selected realizations always have low roundoff noise and small limit cycle bounds.

The response and distribution of maxima of a non-linear oscillator with band limited excitation

The response of an oscillator with a non-linear spring is considered when the excitation force is white noise filtered through a first order low pass filter. When the damping is light, one term in the Fokker-Planck equation for the joint density function of displacement, velocity and acceleration is negligibly small. The resulting approximate Fokker-Planck equation can be solved exactly. An equivalent damping that keeps the power input to the oscillator constant is used to extend the range of validity of the approximate solution. A density function for the distribution of maxima is obtained that covers both narrow band and broad band response. A numerical example of the non-linear maxima distribution is calculated for the case of an oscillator with a bilinear spring.

Eye movement dynamics in the dogfish.

A method is described of obtaining the relationship between electrical stimulation of the abducens nerve and horizontal eye movement in the dogfish. The stump of the VIth nerve was stimulated intracranially in a fish in which the brain had been removed, but in which the circulation remained intact, and the gills were perfused with sea water. Horizontal rotation of the eye was monitored with an opto-electronic movement detector. Eye rotation was linearly related to stimulus frequency in the 0-20 Hz range, and was maximal at frequencies above 40 Hz. Stimulation of the VIth nerve, with a pulse train whose frequency was modulated sinusoidally between 0 and 20 Hz, produced sinusoidal eye movements. The frequency response of the system approximates a first order low pass filter with a characteristic frequency of 0.23 Hz, and an additional phase lag equivalent to a time delay of approximately 50 ms.

Rc-element analysis for low-pass filter and analog differentiator circuits using a programmable calculator

A program written for the Texas Instrument T1-59 programmable calculator is presented. The program will calculate for any biologically important time constant the RC-elements of a second order low pass filter and an analog differentiating amplifier, which are used in biomechanical measuring equipment to study the force of contraction of muscle tissue under various conditions i.e. electrical or chemical stimulation.

Acoustic antialiasing filter having one resistive element for digitized microphone.

The synthetic method of electrical passive networks is successfully applied to the development of an acoustic antialiasing filter for an electret condenser microphone. The Butterworth type lowpass filter of order nine is realized as a tandem connection of an acoustic filter of order five and an electronic filter of order four which is imbeded in the microphone amplifier. The merit of this synthetic design is that the filter can be so realized with only one acoustic resistance that makes the adjustment at the production easy.

Optimalisation du filtrage electronique inverse en microcalorimetrie a conduction

In this paper, the recent development of an electronic inverse filtering system for conduction calorimetry is described: by connecting a second order low-pass filter to the compensating networks, one obtains a better signal without affecting the efficiency of the inverse filter. We report here the optimal conditions for the use of the electronic inverse filtering.

A comparison of switched capacitor network analyses

This paper examines two approaches for the analysis and design of switched capacitor networks. One is based on s-z transformations, and the other one on nodal analysis. A first order lowpass filter is mod for illustration. Results show interesting differences between these approaches.

Integrated CMOS SC filter with 170 kHz cutoff frequency

Based on the theory of switched capacitor (SC) filters using voltage invertor switches (VIS) a third order lowpass filter has been designed and integrated in a standard CMOS metal gate technology. The filter uses a bottom plate stray-insensitive VIS and requires only unity gain buffers. Performance parameters of an integrated version are: cutoff frequency 170 kHz, dynamic range 70 dB, and power dissipation 12 mW.