Signal Feedthrough Research Articles

A differential photoconductive AND gate with Be-doped low-temperature-grown InGaAs-InAlAs MQW MSM-PD's

A novel photoconductive AND gate that overcomes the problems of: 1) the long tail of photoconductive switches and 2) signal leakage via switch capacitance (signal feedthrough) is proposed. We use Be-doped low-temperature (LT)-grown InGaAs-InAlAs MQW metal-semiconductor-metal photodetectors (MSM-PD's) to get a shorter turn-off time and propose a differential AND gate to cancel the signal feedthrough. A comparison between LT-grown MSM-PD's and those fabricated by ion implantation shows that the LT-grown ones are ultrafast with a full width at half maximum of 5.3 ps and are suitable for low-bias operation. It is experimentally confirmed that the differential AND gate completely cancels the signal feedthrough in the picosecond region. The differential AND gate: with the LT MSM-PD's achieves return-to-zero (RZ) 20 Gb/s AND operation.

Differential MSM photoconductive-switch-typesample and hold circuit for reducing signal feedthrough

An MSM photoconductive-switch-type sample and hold circuit having a differential configuration is proposed. Signal feedthrough, which has been one of the most serious problems with the conventional MSM-S/H, is reduced to a common mode signal in this configuration. An experimental comparison between the proposed MSM-S/H and conventional circuits demonstrates that the signal feedthrough is improved from 6% of signal amplitude to less than 1% under the experimental conditions for a 10.2 MHz input.

The ring core fluxgate sensor null feed-through signal

The fluxgate null feed-through signal is discussed theoretically giving an expression for the excitation current and for the core flux coupling coefficients to the secondary coil. Experimental results show that the two signals cannot be nulled simultaneously by rotating the core inside the secondary coil, and give the two coupling coefficients. The excitation current coupling depends critically on the symmetry of the winding, and it is shown that the two signals are associated with excess noise adding to the basic core noise.

Deuterium quadrupole echo NMR spectroscopy II. Artifact suppression

Artifacts which cannot be removed from quadrupole echo spectra by phase cycling can be distinguished from the desired echo on the basis of their response, or lack thereof, to the refocusing pulse. In particular, the phase of the virtual FID or feedthrough signal is determined exclusively by the phase of the first 90° pulse in the 90 x - τ-90 y sequence. At the peak of the echo, therefore, the phase of the virtual FID varies with r, while that of the echo does not. Two procedures are described which make use of this phenomenon to eliminate contributions of the virtual FID to the echo lineshape. In addition an interpolation procedure is described which in effect permits a data set to be left-shifted by fractions of a dwell time, so that the first data point can be placed exactly at the top of the echo.

A.C. performance of f.e.t. analogue switch

The a.c. performance of a series f.e.t. analogue switch is investigated, and it is shown that this choice of switch is not always ideal; since, in the ‘off’ state, signal feedthrough occurs, while, in the ‘on’ state, turnoff of the device can occur past a critical frequency (i.e. frequency pinchoff). Signal feedthrough is easily reduced to negligible proportions by using shunt/series switching; however, frequency pinchoff is shown to be very difficult to eliminate completely. This is especially true when analogue-signal levels are large, and fast switching is required. Therefore, in such circumstances, the technique of elimination is shown to be the restriction of operation to frequencies below the pinchoff frequency. Graphical data are presented which allow this frequency to be determined, and experimental work has confirmed its accuracy.

A gated linear chain

The linear chain described here has been studied to process positive current pulses. The chain can be used as a fast linear gate, when timing and shape information of the pulses have to be preserved, allowing further processing at high repetition rates (up to 20 Mc/sec), or it can be used as a gated integrator with a short dead time. The gate, which is essentially a current transducer, exhibits a linear response with pulses whose amplitude is ranging from ≈0 to about 6 V, with a linearity better than 1%. The pedestal amplitude can be minimized to less than 0.5 mA without affecting the opening and closing times of the gate (≈6 ns for 90% transmission of total charge). The signal feed-through is less than 20 mV at an input signal of ≈ 14 V (rise time less than 1 ns).

High-speed gating circuit using the E8OT beam deflection tube

This paper describes a high-speed gate circuit for an information sampling system employing the E8OT beam deflection tube. The time required to open this gate fully is less than 7 milli-microseconds. This gate is superior to conventional multigrid gates in that the circuits are less complex, more reliable and have only minimal signal feed-through. Furthermore, a preliminary stage of pulse stretching is available without additional circuit elements.