British Aerospace Public Limited Company

British Aerospace Plc

John A Geen

Brian A Johnson

David J Guppy

Peter C Ridgway

Analog-to-digital converters are subject to errors including the known half least significant bit quantization error and also bit weighting errors due to lack of an ideal binary relationship between the transition points of all the bits. The known statistical average error reduction method in which a relatively small dither component is added to the analog input signal can only fractionally reduce overall error and has little effect on bit weighting errors. Herein the analog signal is added to a dither signal, for example a ramp signal, which varies through half the peak to peak digitization range of the converter so that irrespective of the input signal all output signal bits, other than the most significant bit, are 'on' for one half of the sampling period. The result is that all the less significant bit errors are cancelled leaving only the easily compensated most significant bit error. A random component can be added to the dither signal to reduce the quantization error.

Analog-to-digital conversion

Analog-to-digital conversion apparatus with dither signal

In a multiple axis ring laser gyroscope in which one or more of the laser cavity corner mirrors is or are shared by different cavities and in which the laser beams in these different cavities operate at the same nominal frequency, scattering of the beam in one cavity into another cavity by the shared mirror(s) may produce disadvantageous lock-in effects. To at least lessen this possibility, the frequencies of the beams in the gyroscope disclosed herein are offset one from another, the offset being sufficient to affect lock in but not so great that the frequency of any beam is overly far from the lasing medium gain curve center. The frequency offsets may be produced by introducing offset bias signals into some channels of the gyroscope path length control servosystem.

Multiple axis ring laser gyroscopes

A ring laser gyroscope may be oscillated or dithered about its sensing axis to the known `lock-in` effect. The diether motion can comprise an alternating component plus a random component generated by a random noise generator, e.g. a noise diode. The use of a true random noise generator may not always be practicable. Herein, there is proposed the dithering of a ring laser gyroscope with a motion including a component having a specifically Gaussian probability density. Such a component can be formed using a so-called pseudo-random sequence generator based on a shift-register.

Ring laser gyroscopes

A ring laser gyroscope has noise reduction means which removes or compensates for errors which result when a bias or dither is imparted to the gyroscope in order to reduce or avoid lock-in. In one embodiment the gyroscope has processing means (25) including two photodiodes (26,27) which are exposed to the fringe pattern of the gyroscope output beams and which, by the use of a Norton input operational amplifier (30) configured as an electronic integrator, produce a signal which is algebraically summed with the uncorrected gyroscope output signal to produce a corrected gyroscope output signal.

Dithered ring laser gyroscope with residual lock-in error compensation

Detection means comprise at least three photodiodes 1, 2 and 3 which are spaced so as to expand to half a wavelength of an interference waveform produced in a ring laser gyroscope. The three photodiodes 1, 2 and 3 produce respective currents A, B and C the magnitudes of which are detected to sense the magnitude and direction of the movement of the interference waveform. The currents A, B and C are fed to a current mirror configured as a Norton amplifier input state 4, the latter producing signals which are fed to logic circuitry for obtaining signals representative of the rate and direction of the movement of the interference waveform.

Detection of movement of a cyclic interference waveform, such as in a

An oscillatory drive mechanism for a member to be driven comprises a flexural element (12) having a first portion (14) rigidly attached to a datum with respect to which the member is to be driven, and a second portion (15) rigidly attached to the member, the first and second portions (14,15) being interconnected by one or more first interconnecting members (17) which in the main determine the spring characteristics of the flexural element (12), and one or more second interconnecting members (18) having a dimension, generally in the direction of drive, less than the corresponding dimension of each first interconnecting member (17) and at least one of the second interconnecting members (18) having drive means (21) attached which, when energized, flexes the associated second interconnecting member, which in turn moves the second portion (15) of the flexural element relative to the first portion (14) so as to oscillate the driven member.

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Bracknell, United Kingdom

John A Geen