U.S. Philips Corporation

Koninklijke Philips Corporation N.v.

Andreas H Wichern

Knud Holtvoeth

Christoph G Leussler

Burkhard Dick

Anthony H Richards

Niels Gabriel

Wilfried E Knop

A gain-controlled amplifier comprises two signal output stages arranged in parallel to drive an output load in series. A maximum-gain stage provides a maximum of signal gain and the other minimum-gain stage fixes the minimum overall amplifier signal gain. Gain-control input signals differentially applied to the two such stages balance the contributions of the respective gain stages delivered to the common output load. In one aspect, a third shunting transistor is used across the minimum-gain stage. In another version, the output load is a tapped resistor and the respective maximum and minimum gain stages drive different taps.

Gain-controlled amplifier with fixed minimum gain

Circuit arrangement

In a circuit arrangement for rectifying a signal, in which two transconductors are controllable with opposite phase by means of the signal to be rectified, the outputs of the transconductors are connected to a first circuit point via a first diode and to a second circuit point via a second diode having an opposite polarity with respect to the first diode. The circuit points are connected to a predetermined potential. A rectified signal can be derived from at least one of the circuit points.

Circuit arrangement for rectifying a signal

An oscillator arrangement is described including a resonant circuit having two poles from which an oscillation generated in the oscillator arrangement can be taken and including a differential amplifier of two emitter-coupled transistors having two collector electrodes of which each one is connected to one of the poles of the resonant circuit, and having two base electrodes cross-coupled to the poles of the resonant circuit. Such an oscillator arrangement can be constructed so as to generate a low-noise oscillation by means of a minimal number of circuit elements in that the base electrodes are each coupled to the poles of the resonant circuit via a diode configuration.

Oscillator with cross-coupling by diodes

A radio receiver having a double-balanced mixer stage comprising two pairs of emitter coupled transistors (T,to T,), the common emitters of each pair of transistors being connected to identical current sources (T,, T,and T,). A local oscillator signal is applied differentially to junctions (,) of the base electrodes of the first and fourth transistors (T,, T,) and the second and third transistors (T,, T,), respectively. The rf input signal is applied to the common emitter junctions (,) via damping resistors (R,, R,) which also are connected to respective current sources. Outputs from the pairs of emitter coupled transistors are coupled to cascode stages (,). Further damping resistors (R,, R,) are connected between the differential local oscillator input (,A,,B) and the junctions (,) of the base electrodes. The damping resistors are of a low value typically 25 ohms and serve to stabilize the double-balanced mixer circuit and prevent it from going into oscillation.

Radio receiver with a double-balanced mixer circuit having signal damping elements

A receiver has a crystal oscillator (10) whose frequency can be adjusted in response to temperature compensation (TC) and automatic frequency control (afc) signals. The TC and afc signals are summed and applied to an op-amp (70) having a fixed gain functioning as a current to voltage converter. An output of the op-amp (70) is applied to the crystal oscillator (10). If the receiver is switched--on and--off in accordance with say a time division protocol, the output of the op-amp (70) is applied by way of a switch (72) to a storage circuit (30,C) which when the switch is open applies a bias voltage on the crystal oscillator (10) to maintain its output frequency.

Radio receivers

Circuit arrangement for producing a D.C. current

A circuit arrangement having an input arranged to receive an input signal (U20) and an output for providing an output signal (U22). The circuit has an overall transfer function defined as the ratio between the output signal and the input signal and which is obtained by adding individual transfer functions of at least two different amplifiers with different slopes in their linear ranges and/or different limit values in their saturation ranges and/or different zero points alternately with positive and negative signs in a manner such that, at least partly, it corresponds substantially to a function of at least the third degree. This circuit arrangement generates, in a simple manner, an overall transfer function of at least the third degree, which can be used advantageously, for example, for the compensation of the temperature-verses-resonant-frequency characteristic function of a quartz crystal.

Circuit having overall transfer function providing temperature

A high frequency amplifier circuit arrangement has an output current path having one end coupled to a reference potential for supplying an alternating signal current at an output terminal. The influence of parasitic inductances in the output current path on the amplitude of the alternating signal current is reduced or cancelled in that compensation is provided for the influence of a parasitic inductance in the coupling between the output current path and the reference potential by means of a compensation circuit which applies an alternating compensation current to a (first) node between the output current path and the parasitic inductance. This compensation current is in phase opposition to and of at least substantially the same magnitude as the alternating signal current.

Circuit arrangement for supplying an alternating signal current

A surface coil for magnetic resonance examinations is formed by two longitudinal conductors and a plurality of transverse conductors which interconnect the longitudinal conductors in a plane. A coupling device couples the coil to an RF transmitter or an RF receiver. An RF magnetic field is produced by the coil parallel to the plane defined by the transverse conductors. The transverse conductors each include at least one capacitor. One of the two outer transverse conductors forms a part of the coupling device. The conductors and the capacitors are proportioned and have values so that the current through the outer transverse conductor forming a part of the coupling device is uniformly distributed between the other transverse conductors.

Surface coil for magnetic resonance examinations

An MR examination apparatus has a quadrature coil arrangement which consists of two coil systems and a circuit for decoupling the two coil systems. In such an MR examination apparatus the decoupling between the coil systems is improved in that the circuit comprises a variable capacitor which connects one coil system to the other.

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Hamburg, Germany

Andreas H Wichern