Abstract: An electronic metal detector having a transmit coil (1) adapted to transmit an alternating magnetic field associated with a reactive transmit voltage, wherein the transmit voltage signal is selected such that the reactive transmit voltage is approximately constant for at least a time period during which a magnetic field signal to be processed is received by the detector for processing.

Abstract: This invention relates to an electronic metal detector having transmit electronics comprising switching electronics arranged and adapted to generate a transmit signal, the transmit electronics comprising at least two power sources, a first power source and a second power source, the transmit electronics being connected to a transmit coil arranged and adapted to transmit an alternating magnetic field, wherein the switching electronics are adapted and arranged to switch a first voltage of the first power source to the transmit coil for at least a first period and also a third period, the switching electronics being adapted and arranged to switch a second voltage of the second power source to the transmit coil for at least a second period.

Abstract: An electronic class-D amplifier with intrinsically low distortion employing modulation of the slopes of a triangular-wave carrier reference signal; the modulation being in proportion to the derivative of the input signal. The negation of the distortion is most successful if this derivative signal is shifted in phase and gain to compensate for the closed loop phase and gain of the amplifier. The amplifier includes a pulse width modulator which includes an oscillator (5) with at least one integrator and a first comparator (6), at least one servo-loop amplifier (3), an input signal processor (4) which processes and modifies the input amplifier signal. An output signal of the oscillator produces a carrier reference signal (13) which includes at least positive and negati derivative components, which are modulated by an output of the input signal processor (4) which is applied to a modulation input of the oscillator (5), whereby at least the symmetry of the carrier reference signal is modulated.

Abstract: An electronic class-D amplifier including a pulse width modulator and a servo-loop amplifier characterized in that there is provided a sample and hold element which samples a signal at the sample input when a sample command signal is applied to a control input, and holds the value of the last sampled value of the signal at the sample input when a hold command signal is applied to the control input, and the output of the sample and hold element is connected to a modulation input of the pulse width modulator wherein a negative feedback path connects an output of the output switching stage to an input of the servo-loop amplifier.

Abstract: An electronic class-D amplifier including a one servo-loop amplifier plus pulse width modulator, and a controlled delay stage including a delay modulation input, and a negative feedback path connects an output of the output switching stage to an input of the servo-loop amplifier wherein the forward gain of an output switching stage, the forward gain of the servo-loop amplifier plus pulse width modulator and controlled delay stage, and a carrier reference output signal's mean frequency, and modulation gain of the controlled delay stage, and the gain of the negative feedback path, are selected to lower the distortion of a signal at the amplifier output relative to a signal applied to the amplifier input.

Abstract: An electronic class-D amplifier including a pulse width modulator and a servo-loop amplifier characterised in that there is provided a sample and hold element which samples a signal at the sample input when a sample command signal is applied to a control input, and holds the value of the last sampled value of the signal at the sample input when a hold command signal is applied to the control input, and the output of the sample and hold element is connected to a modulation input of the pulse width modulator wherein a negative feedback path connects an output of the output switching stage to an input of the servo-loop amplifier.

Abstract: An electronic class-D amplifier including a one servo-loop amplifier plus pulse width modulator, and a controlled delay stage including a delay modulation input, and a negative feedback path connects an output of the output switching stage to an input of the servo-loop amplifier wherein the forward gain of an output switching stage, the forward gain of the servo-loop amplifier plus pulse width modulator and controlled delay stage, and a carrier reference output signal's mean frequency, and modulation gain of the controlled delay stage, and the gain of the negative feedback path, are selected to lower the distortion of a signal at the amplifier output relative to a signal applied to the amplifier input.

Abstract: An ultra-low distortion electronic amplifier wherein the global dominant pole is formed by the selection of circuit and component arrangement within the input stage, such that the global dominant pole, is of third order, at audio frequencies. This audio power amplifier implements a high order global dominant pole with the use of operational amplifiers, and this high order dominant pole is distributed across both the voltage amplification stage and input stage without adverse reduction in the slew rate. The amplifier has increased negative feedback at audio and ultrasonic frequencies, giving a reduction in distortion across the entire audio band and some of the lower ultrasonic band.

Abstract: Metal detection apparatus containing at least two inductive coils one of which acts as a transmit coil and all of which act as receive coils and processing circuitry wherein a proportion of the first receive electronic signal and a proportion of the second receive electronic signal may be selected to produce various first resultant linear combination signals for the purpose of improved interference cancelling.

Abstract: A metal detector apparatus including a transmit coil which transmits a magnetic field, transmit timing control circuitry which also includes timing for a semiconductor switch, and receive signal circuitry and receive signal processing circuitry, with a transmit coil damping network including at least one resistor connected in series with the semiconductor switch across the transmit coil, and timing control circuitry which generates a timing sequence which is selected so that for at least some of the time no transmit field is generated and at least during part of the transmit signal, the first semiconductor switch is controlled to be off and is turned on before the cessation of the transmit field.

Abstract: A metal detector with a transmit coil which transmits a magnetic field, transmit timing control circuitry, and receive signal circuitry and receive signal processing circuitry, and a low voltage and a high voltage power supply. The timing sequence generated within the transmit timing control circuitry produces control signals such that there are at least two different transmit periods, a short and a long period, and such that there are periods when no current flows through the transmit coil. The timing sequence is such that an average transmit coil energy at termination of the long periods is similar to that of an average transmit coil energy at termination of the short periods.

Abstract: Metal detection apparatus wherein a transmit coil will transmit magnetic pulses, and the processing circuitry will weight a receive signal more heavily soon after a transmit pulse transition and less heavily after a longer period following the transmit pulse transition.

Abstract: An electronic amplifier providing very low distortion which includes an output stage with an output error correction stage containing two amplifiers and wherein there are at least four local negative feedback paths, an output of the first amplifier being connected to an input of output stage transistor buffers or output stage transistors through a first network, an output of the second amplifier being connected to an input of output stage transistor buffers or output stage transistors through a second network, where components of the first and second amplifier the local negative feedback paths, first and second networks and output stage transistor buffers are selected to form substantially second order local dominant pole. Also disclosed is the supply of power to said first and second amplifiers from a floating power supply means coupled to either an or the output of the output stage so that the voltage of the floating power supply will follow substantially an output voltage of the output stage.

Abstract: An amplifier having error correction and including an output stage containing output transistors being connected to the amplifier output, and an output error correction stage containing a first high open loop gain amplifier which includes one or more transistors being the first high open loop gain amplifier transistor or transistors, an output of which is connected to an input of the output stage, the amplifier including at least two local negative feedback paths, a first local negative feedback path being between an output of the output stage and an input of the first high open loop gain amplifier and a second local negative feedback path being between an output of the first high open loop gain amplifier and an input of the first high open loop gain amplifier.

Abstract: This invention is for an improvement in amplifiers resulting in ultra low distortion.

Abstract: This invention is for a pulse induction metal detector which uses combinations of the signal detected during non-transmission of the magnetic field to eliminate those contributions to the signal due to the remanent magnetization of ferrites and asynchronous magnetic fields within the target volume.

Abstract: An apparatus and method for supplying a regulated direct electric current comprises a switch mode regulator having an input for receiving a varying source of electrical power. A linear regulator provides a source of low noise direct current and has an input connected so as to receive a voltage that is dependent upon an output of the switch mode regulator. A first servo-loop provides a first control signal to the switch mode regulator. The first control signal is varied according to a variation in the voltage across the linear regulator. A second servo-loop provides a second control signal to the linear regulator. The second control signal is varied according to the difference between a voltage that is related to an output of the linear regulator and a reference voltage. The second servo-loop has a higher gain than the first servo-loop when both of the servo-loops are operating at frequencies that are within their operating frequency ranges.

Abstract: This invention is for a method of an apparatus to perform metal discriminatory detection comprising the application of a multi period rectangular wave form to a transmitter coil, processing received signals by combining received components measured during different selected periods with respect to the transmitted signal in a manner based upon the predictable characteristics of ground constituents and thereby to provide an output signal which will be selectively indicative of a metal object within a target volume and substantially distinguishable from any signal arising from any electrically non-conducting ferrite in the target volume.