Involving Structure Other Than That Of Transformers Per Se Patents (Class 330/65)
  • Patent number: 9007124
    Abstract: A system for power amplification is presented. A tile array power amplifier (PA) module for use in a phased array includes a module with a radio frequency (RF) side and a direct current (DC) side, a top edge, a left edge a bottom edge and a right edge. Four PA dies are mounted in each quadrature of the RF side of the module. RF input connectors are mounted on the RF side to bring RF inputs to the PA dies. RF output connectors are mounted to the DC side to output amplified signals from the PA dies. The PA dies are formed, in part, with gallium nitride (GaN) and are mounted to the module in such a way that the tile array PA module is able to generate about 100 watts of RF power and dissipate about 200 watts of heat while amplifying signals over 10 GHz.
    Type: Grant
    Filed: September 17, 2013
    Date of Patent: April 14, 2015
    Assignee: BAE Systems Information and Electronic Systems Integration Inc.
    Inventor: James J. Komiak
  • Publication number: 20140218105
    Abstract: An amplifier includes: an amplifying device configured to amplify an input signal; and a matching circuit coupled to the amplifying device, and including an impedance transformer and a parallel resonance circuit coupled to a wiring which spans from the impedance transformer to the amplifying device, wherein a circuit length of the impedance transformer is longer than one-fourth of wavelength of an electronic wave having a frequency which is substantially equal to a resonance frequency of the parallel resonance circuit.
    Type: Application
    Filed: November 14, 2013
    Publication date: August 7, 2014
    Applicant: FUJITSU LIMITED
    Inventors: Nobuhisa AOKI, Toru MANIWA
  • Patent number: 8766714
    Abstract: An amplifier component (1) provides a chip housing (40) and at least two amplifier elements (31, 32). Between at least two connections (51, 52 and 61, 62) of each amplifier element (31, 32), a parasitic capacitance (81, 82) is formed, wherein this parasitic capacitance (81, 82) is compensated by an inductive compensation element (2). The compensation element (2) itself is formed between two connecting contacts (101, 102) outside of the chip housing (40) by a connecting lug (2).
    Type: Grant
    Filed: November 30, 2010
    Date of Patent: July 1, 2014
    Assignee: Rohde & Schwarz GmbH & Co. KG
    Inventor: Bernhard Kaehs
  • Patent number: 7297055
    Abstract: A method of generating a high-level vacuum comprises evacuating a chamber having a substantially-pure gas therein to a medium-level vacuum, and freezing the residual gas to generate the high-level vacuum within the chamber. Impurities, such as atmospheric air, may be purged from the chamber by evacuating the chamber to a medium level vacuum (e.g., around 10?2 Torr) and subsequently filling the chamber with the gas. This purging process may be repeated multiple times to decrease the level of impurities in the gas filling the chamber. The substantially-pure gas may have an impurity-level of less than approximately 100 PPM and may comprise carbon-dioxide, although the scope of the invention is not limited in this respect. The medium level vacuum may range between approximately 1×10?2 Torr and 5×10?2 Torr allowing the use of a roughing pump, and the high-level vacuum may range between approximately 1×10?5 and 1×10?8 Torr.
    Type: Grant
    Filed: March 16, 2004
    Date of Patent: November 20, 2007
    Assignee: Raytheon Company
    Inventors: David R. Sar, Jerry D. Withrow
  • Patent number: 6724250
    Abstract: A transformer of power-amplifier module for an audio device includes a casing having a first plug and a second plug formed thereon. In the casing, there is an amplifying circuit having an input electrically connected to the first plug and an output electrically connected to the second plug of the casing. The amplifying circuit terminates in a transformer at the output. Furthermore, the transformer is adjustable so as to control the amplitude of output voltage of the transformer of power-amplifier module.
    Type: Grant
    Filed: June 12, 2002
    Date of Patent: April 20, 2004
    Inventor: Pao-An Chuang
  • Publication number: 20030231056
    Abstract: A transformer of power-amplifier module for an audio device includes a casing having a first plug and a second plug formed thereon. In the casing, there is an amplifying circuit having an input electrically connected to the first plug and an output electrically connected to the second plug of the casing. The amplifying circuit terminates in a transformer at the output. Furthermore, the transformer is adjustable so as to control the amplitude of output voltage of the transformer of power-amplifier module.
    Type: Application
    Filed: June 12, 2002
    Publication date: December 18, 2003
    Inventor: Pao-An Chuang
  • Publication number: 20030222710
    Abstract: An amplifier housing assembly is disclosed. The housing assembly includes a first section including a first plurality of holes; and a second section including a second plurality of holes. The first and second sections are interconnected. The first and second sections have a common back wall and a common bottom plate. The first plurality of holes and the second plurality of holes are at two different parallel planes.
    Type: Application
    Filed: May 31, 2002
    Publication date: December 4, 2003
    Inventors: Jay Lee, Ben Newell
  • Patent number: 6614311
    Abstract: A micro-wave power amplifier which amplifies a micro-wave signal including a plurality of carrier frequencies different from one another, includes (a) a field effect transistor having a grounded source, (b) a first difference frequency circuit which is electrically connected to a drain of the field effect transistor, and is short-circuited at a difference frequency between the carrier frequencies, and (c) a second difference frequency circuit which is electrically connected to a gate of the field effect transistor, and is short-circuited at a difference frequency between the carrier frequencies.
    Type: Grant
    Filed: November 29, 2001
    Date of Patent: September 2, 2003
    Assignee: NEC Compound Semiconductor Devices, Ltd.
    Inventor: Isao Takenaka
  • Patent number: 6518844
    Abstract: A suspended transmission line with an embedded amplifier includes a support layer and a conductor supported on the support layer between first and second plates each having a ground plane. The conductor includes an input section and an output section. A propagation structure is disposed between the first and second plates to substantially encompass an electric field generated by a signal transmitted on the conductor. An amplifier is coupled to the input and output sections of the conductor and is at least substantially disposed between the first and second plates. The amplifier operates to amplify an input signal received on the input section to generate an output signal on the output section.
    Type: Grant
    Filed: April 13, 2000
    Date of Patent: February 11, 2003
    Assignee: Raytheon Company
    Inventors: James R. Sherman, Ofira M. Von Stein
  • Patent number: 6396342
    Abstract: A microwave amplifier includes an amplifying device having a first contact region extending in a width direction, an output side impedance device spaced from the amplifying device in a transmission direction perpendicular to the width direction, the impedance device having a second contact region connected to the first contact region of the amplifying device, the second contact region extending in the width direction, and a smoothing circuit connected to one of the first and second contact regions for smoothing a distortion in a microwave signal to be amplified by the amplifying device.
    Type: Grant
    Filed: October 12, 2000
    Date of Patent: May 28, 2002
    Assignee: NEC Corporation
    Inventor: Isao Takenaka
  • Patent number: 6388892
    Abstract: A tuner unit includes a unit board. The unit board is formed, at its lower end, with a protrusion to have a terminal pattern formed on the protrusion. A frame chassis has a side plate having, at its lower end, a protrusion having a tapered side face in one of side faces. When the protrusion of the unit board is inserted in a hole of a main board, the tapered side face is inserted while abutted against an inner edge of a hole of the main board. This urges the protrusion in a direction that the terminal pattern is brought close to the connection pattern of the main board.
    Type: Grant
    Filed: April 4, 2000
    Date of Patent: May 14, 2002
    Assignee: Funai Electric Co., Ltd.
    Inventor: Osamu Maeda
  • Patent number: 6300827
    Abstract: A cascaded amplifier is integrated within an integrated circuit with a cascaded ground bus. The cascaded ground bus provides two ground points at opposite ends. Each amplifier ground of each amplifier stage couples to the ground wire there between. The cascaded ground bus substantially reduces the parasitic inductance in the emitter leg of each IC transistor within each amplifier. The lay out of the cascaded ground bus wire is tightly coupled to the lay out of the input wires so that their respective parasitic inductances are magnetically coupled together to form a mutual inductance. The mutual inductance effectively cancels the effect of the ground return inductance due to them being similar inductance values and having the same ground loop current flowing through them in opposite directions.
    Type: Grant
    Filed: December 9, 1999
    Date of Patent: October 9, 2001
    Assignee: Maxim Integrated Products, Inc.
    Inventor: Joel King
  • Patent number: 6259901
    Abstract: A radio-frequency power amplifier of mobile communication equipment includes a differential amplifier arranged to balanced-input and amplify a radio-frequency signal delivered from a frequency converter of a transmission system of the mobile communication equipment located downstream of a modulator of the transmission system. The radio-frequency signal delivered from the differential amplifier is further amplified and balanced-output by a push-pull circuit. The differential amplifier and the push-pull circuit are respectively supplied with bias currents varying in dependence on a gain control signal, whereby respective amplification gains of the differential amplifier and the push-pull circuit are variably adjusted.
    Type: Grant
    Filed: December 1, 1998
    Date of Patent: July 10, 2001
    Assignee: Mobile Communications Tokyo Inc.
    Inventors: Yoshitaka Shinomiya, Takeshi Imai
  • Patent number: 5726605
    Abstract: An RF power amplifier module utilizing a plurality of silicon carbide transistor power amplifier circuits, each including a transistor assembly having multiple cells, respectively providing power amplification of an input signal. In a preferred embodiment of the invention, four mutually staggered silicon carbide transistor assemblies, each containing multiple transistor cells, are operated in parallel while being arranged in close proximity on a common substrate. Each silicon carbide amplifier circuit assembly is commonly driven by a fifth silicon carbide amplifier circuit. The outputs of the parallely driven silicon carbide transistor power amplifier circuits are combined so as to provide a single composite RF output signal which may be in the order of 1000 watts or more when operated at a frequency of, for example, 600 MHz.
    Type: Grant
    Filed: April 14, 1996
    Date of Patent: March 10, 1998
    Assignee: Northrop Grumman Corporation
    Inventors: Alfred W. Morse, Paul M. Esker, Robin E. Hamilton
  • Patent number: 5719526
    Abstract: A load monitor module for measuring voltage and current supplied from an amplifier to a load is provided within an amplifier and includes a device for calculating an impedance of the load and an amount of power delivered to the load from the amplifier. The load monitor module includes a voltage measuring device and a current measuring device for accurately measuring the voltage and current of a generated test signal or an audio signal input the amplifier signal path without substantially altering the signal. The monitor module also includes a controller for controlling the performance of the amplifier and load according to the calculated load impedance and power input to the load from the amplifier.
    Type: Grant
    Filed: November 16, 1995
    Date of Patent: February 17, 1998
    Assignee: Crest Audio, Inc.
    Inventor: Dennis Fink
  • Patent number: 5663683
    Abstract: A mist cooled distributed amplifier utilizing a connectorless module. The amplifier comprises modules that are connected to waveguides in a honeycomb. The RF signals are distributed to and combined from the modules using a distributed waveguide manifold. Cooling is accomplished by forming channels between the modules through which mist is transmitted and collected and condensed at the output end.
    Type: Grant
    Filed: December 18, 1995
    Date of Patent: September 2, 1997
    Assignee: The Boeing Company
    Inventor: Jay H. McCandless
  • Patent number: 5652544
    Abstract: An apparatus and method for programming an amplifier includes an amplifier and a portable programmer that is removably connectable to the amplifier. The portable programmer includes a microprocessor, a keypad, and a display screen. The amplifier includes a programming input port, a signal processing circuit, a power amplifier and a control circuit. When the portable programmer is connected to the amplifier, information relating to parameter of various signal processing circuit elements can be read and modified through the programmer. The information input via the keypad and displayed on the display screen is transmitted from the programmer via the microprocessor to the signal processing control circuit to change signal processing functions and/or signal process function parameters of at least one of the signal processing circuit elements. As a result, processing of a signal transmitted through the amplifier is changed so that a sound produced by the signal can be modified.
    Type: Grant
    Filed: November 16, 1995
    Date of Patent: July 29, 1997
    Assignee: Crest Audio Inc.
    Inventor: Dennis Fink
  • Patent number: 5491449
    Abstract: A Dual-Sided Push-Pull Amplifier for providing a high-gain yet low-cost amplifier capable of operating at frequencies extending above 1 GHz is disclosed. The present invention may be used in any application in which low cost amplification may be desired, including transmitters, antenna arrays, radars, light wave modulators, mixers, local oscillators, driver amplifiers and microwave ovens. One of the preferred embodiments of the invention (10d/10e) utilizes two pairs of field effect transistors (FETs) (22U and 22L & 24U and 24L) mounted in registration on both faces (12a & 12b) of a dual-sided dielectric substrate (12). The sources (22US and 22LS & 24US and 24US) on both faces of the FETs (22 & 24) are electrically coupled and are located at a minimum distance from their mates on the opposite faces of the substrate (12) to reduce inter-FET source lead inductance. The FETs (22 & 24) are coupled to a set of conductors (16a, 16b, 16c & 16d) which are formed on the substrate (12).
    Type: Grant
    Filed: November 19, 1993
    Date of Patent: February 13, 1996
    Assignee: Endgate Technology Corporation
    Inventors: Edwin F. Johnson, Douglas G. Lockie, Clifford A. Mohwinkel
  • Patent number: 5352991
    Abstract: A power amplifier assembly that dissipates a maximum of one thousand one hundred watts includes a power amplifier circuit and a chassis that has an overall volume of 0.02 cubic meters. The chassis includes a heat sink base that contains a mounting pattern for the power amplifier circuit. By thermally coupling the power amplifier circuit to the heat sink base via thermal coupling devices and the mounting pattern, the heat sink base dissipates a maximum of one thousand one hundred watts in a volume of 0.016 cubic meters.
    Type: Grant
    Filed: August 12, 1993
    Date of Patent: October 4, 1994
    Assignee: Motorola, Inc.
    Inventors: Jeffrey S. Lipschultz, John N. Lubbe, Marc H. Pullman
  • Patent number: 5208554
    Abstract: A Class A high power amplifier having an operating frequency in the range of less than substantially 2 GHz and suitable for aircraft use, is all solid state in that gallium arsenide field effect transistors are utilized. These are mounted in a large copper heat sink which is air cooled to provide for overall cooling by conduction and convection. By the use of microstrip matching circuits, the relatively low impedance of the gallium arsenide FET units is matched to the required higher system impedance. At the same time a 40% band-width is provided due to the superior matching.
    Type: Grant
    Filed: January 24, 1992
    Date of Patent: May 4, 1993
    Assignee: Systron Donner Corporation
    Inventors: Harvey Endler, Hadi Mojaradi
  • Patent number: 5130891
    Abstract: An amplifier housing assembly particularly useful for automobile stereo systems is disclosed. The assembly comprises a mounting plate which bolts to a stationary surface and an amplifier enclosure which mounts on the mounting plate. Wires from speakers and a power source are connected to the mounting plate which are then connected to the amplifier when the amplifier housing is mounted on the mounting plate by means of male and female connectors. An antitheft feature of the housing is that the mounting bolts of the mounting plate are rendered inaccessible when amplifier enclosure is mounted on the mounting plate.
    Type: Grant
    Filed: January 2, 1991
    Date of Patent: July 14, 1992
    Assignee: Infinity Systems, Inc.
    Inventor: Cary L. Christie
  • Patent number: 5087888
    Abstract: A way of constructing modular RF power amplifiers. RF power amplifiers are constructed of a standardized chassis plus a number of RF power modules with each such power module containing provisions for self-cooling.
    Type: Grant
    Filed: July 26, 1990
    Date of Patent: February 11, 1992
    Assignee: Motorola, Inc.
    Inventors: Michael C. Mountz, Peter A. Kwitkowski
  • Patent number: 4963833
    Abstract: An improved high powered power amplifier, where the improvement comprises an improved grounding technique by decreasing the contact resistance, and an improved thermal transfer and dissipating technique. The heat generated by a power amplifier device is transferred and dissipated substantialy outside a chassis and is in direct contact with a heat sinking device located outside the chassis. By having the heat transfer and heat dissipation occurring outside the chassis and by having the power amplifier device in direct contact with the heat sinking device, the power amplifier is capable of reliably operating at higher power levels.
    Type: Grant
    Filed: June 12, 1989
    Date of Patent: October 16, 1990
    Assignee: Motorola, Inc.
    Inventor: Michael C. Mountz
  • Patent number: 4901029
    Abstract: A power amplifier arrangement incorporating a plurality of amplifier units and a power supply unit includes a cooling arrangement that is efficient and results in compactness of the overall power amplifier arrangement. The amplifier units and power supply unit are slideable on a shelf through the use of guiderails. Connecting means of the plug-socket type are utilized for connecting the amplifier units with the power supply unit. Cooling air chambers are disposed adjacent to the amplifier units and include nozzles directed onto a radiation plate on which heat-producing amplifier devices are mounted.
    Type: Grant
    Filed: September 14, 1988
    Date of Patent: February 13, 1990
    Assignee: NEC Corporation
    Inventors: Kazuo Fujino, Tetsumichi Yamamoto, Tomohito Ikegami, Takeshi Yanagibayashi
  • Patent number: 4864245
    Abstract: A modification unit for a musical instrument amplifier includes a modification circuit and a connector for connecting the modification circuit to a tube socket in place of one of the tubes in the pre-amp stage of the amplifier. The pre-amp includes at least a gain stage with a gain tube and a socket for receiving the gain tube where the tube socket has at least one plate contact, at least one cathode contact and at least one filament (heater) contact. The modification circuit includes a jack for receiving an electronic signal originated by the musical instrument and a circuitry for modifying the received electronic signal to generate a modified signal.
    Type: Grant
    Filed: November 22, 1988
    Date of Patent: September 5, 1989
    Assignee: Kasha Amplifiers
    Inventor: John Kasha
  • Patent number: 4751471
    Abstract: An amplifying circuit for amplifying a bipotential input signal, including an insulating housing having a conductive input contact mounted on the housing and adapted to engage a human body so that the bipotential input signal applied to the contact; a lead amplifier having inverting and non-inverting inputs, one of which is coupled to the input contact, and an output; first and second diodes connected in parallel inverse polarity across the inputs of the lead amplifier; third and fourth diodes connected in parallel inverse polarity from the inverting input of the lead amplifier to a circuit common potential; and an output resistor connected from the inverting input to the output of the lead amplifier. Portions of the input contact are surrounded by a voltage drive shield connected to the output of the lead amplifier.
    Type: Grant
    Filed: December 23, 1986
    Date of Patent: June 14, 1988
    Assignee: Spring Creek Institute, Inc.
    Inventor: W. J. Ross Dunseath, Jr.
  • Patent number: 4471314
    Abstract: A high power single or multichanneled pulse width modulated (PWM) audio amplifier is fabricated in a single package using hybrid assembly techniques.
    Type: Grant
    Filed: June 15, 1981
    Date of Patent: September 11, 1984
    Inventor: Charles R. Lindberg
  • Patent number: 4342002
    Abstract: An amplifier system comprises a plurality of modules located within a cabinet in a manner providing minimum signal paths. The signal to be amplified is divided into frequency ranges for main amplification, and each main amplifier has an independent power supply. The modules are constructed from extrusions shaped and assembled to facilitate servicing and to function as heat sinks or as a cooling system as well as to provide mechanical protection and electrostatic shielding.
    Type: Grant
    Filed: February 8, 1980
    Date of Patent: July 27, 1982
    Assignee: A.R.D. Anstalt
    Inventor: Saad Z. M. Gabr
  • Patent number: 4223272
    Abstract: A four-terminal network selectively convertible into a low-pass, high-pass, band-pass, all-pass or band-stop filter comprises three cascaded stages each including an operational amplifier with a grounded noninverting input, the amplifiers of the first two stages being of the integrating type provided with capacitive feedback circuits. Resistive feedback connections extend from a main output A of the third stage to the inverting inputs of the first and third stages and from a relatively inverted output A' of the third stage to the inverting input of the second stage, their respective resistances R.sub.u, R.sub.v, R.sub.w determining the coefficients of the denominator in a biquadratic equation ##EQU1## where H(p) is the transfer function of the network and p=jf/f.sub.n is given by the ratio of an operating frequency f to a reference frequency f.sub.o. The coefficients of the numerator, which could be of either sign and may also be zero, are determined by supply resistances R.sub.a, R.sub.b, R.sub.
    Type: Grant
    Filed: October 25, 1978
    Date of Patent: September 16, 1980
    Assignee: Wandel & Goltermann GmbH & Co.
    Inventor: Karl H. Feistel
  • Patent number: 4214214
    Abstract: A connecting cable comprising a length of coaxial cable having at one of its ends an input plug connector whose first and second input terminals are adapted to connect to the electrical output terminals of a pickup of a musical instrument, and means comprising a field effect transistor connected in the circuit of the cable and connector and housed within the connector.
    Type: Grant
    Filed: August 3, 1978
    Date of Patent: July 22, 1980
    Inventor: George W. Merriman
  • Patent number: 4151479
    Abstract: A low frequency power amplifier uses MOS FET's each having a semiconductor device unit including a source electrode, a drain electrode and an insulated gate electrode filled in a can type casing with the source electrode being electrically connected to the can type casing. When the MOS FET having its source electrode connected to the can type casing is mounted on a heat sink and operated in a source follower configuration, a stray capacity between the can-shaped casing and the heat sink is connected in parallel with a load so that the amplifier oscillates. The heat sink is grounded through an impedance element and the stray capacity is isolated from the load to prevent the oscillation.
    Type: Grant
    Filed: April 13, 1978
    Date of Patent: April 24, 1979
    Assignee: Hitachi, Ltd.
    Inventor: Tatsuo Baba
  • Patent number: 4134077
    Abstract: An amplifier circuit having stable performance characteristics over a wide temperature range from approximately C up to as high as approximately C, such as might be encountered in a geothermal borehole. The amplifier utilizes ceramic vacuum tubes connected in directly coupled differential amplifier pairs having a common power supply and a cathode follower output stage. In an alternate embodiment, for operation up to C, positive and negative power supplies are utilized to provide improved gain characteristics, and all electrical connections are made by welding. Resistor elements in this version of the invention are specially heat treated to improve their stability with temperature.
    Type: Grant
    Filed: October 20, 1977
    Date of Patent: January 9, 1979
    Assignee: System Development Corporation
    Inventors: Ronald D. Kelly, William L. Cannon
  • Patent number: 4124877
    Abstract: In electronic amplifiers it is desirable to have the capability of accurate setting of the characteristic values while still having a limited space on a front panel. In order to accomplish this, a digital switch having a plurality of digital switch units on a front portion is coupled to an amplifier assembly. The amplifier assembly is coupled to the back portion of the digital switch and has a configuration such that it can fit into the same opening in the panel as the digital switch alone. Thus, the entire electronic amplifier unit takes up no more frontal space on the panel than that necessary for mounting the digital switch alone.
    Type: Grant
    Filed: April 25, 1977
    Date of Patent: November 7, 1978
    Assignee: Kistler Instrumente AG
    Inventor: Max Vollenweider
  • Patent number: 4059810
    Abstract: A metal plate carrying a semiconductive chip with a five-terminal power amplifier is encased in a prismatic resinous body having five tongues projecting from one side thereof, the central tongue being grounded to the plate while the other four are attached to various terminals of the chip. The projecting portions of the five tongues are alternately bent angularly in opposite directions to increase the separation of their free ends. During assembly, a connector strip bearing a number of five-tongue groups is fitted onto a support strip, divided into as many plate sections, by inserting a bent-over extremity of the central tongue of each group, provided with an enlarged head, into a recess of a confronting plate section preparatorily to encasement.
    Type: Grant
    Filed: March 29, 1976
    Date of Patent: November 22, 1977
    Assignee: SGS-ATES Componenti Elettronici SpA
    Inventor: Raimondo Paletto
  • Patent number: 4055809
    Abstract: Various types of repeaters which are requisite in combination for making electrical networks such as CATV or MATV systems are unified into a common or universal repeater enabling three fundamental performances comprising a trunk line junction, a branching junction and a distributing junction each use of which is selectively determined by changing connective angles of two plugs containing a branching circuit and a distributing circuit, respectively.
    Type: Grant
    Filed: April 13, 1976
    Date of Patent: October 25, 1977
    Assignee: Hochiki Corporation
    Inventors: Takeshi Takeuchi, Mitsuo Takahashi
  • Patent number: 3940666
    Abstract: A circuit module, such as is used in a modular L-C filter, includes a support having a base portion and side portions. One or more electric circuit elements, such as inductors and capacitors, are mounted on the support. One of the side portions of the support is provided with an externally exposed recess which is adapted to at least partially receive an interconnecting element such as a coupling coil. Thus, two of the modules can be located on a circuit board in adjacent relationship with the recesses therein aligned to form a cavity in which the coupling coil is received, the coil itself preferably being independently mounted on the circuit board. In this manner, the amount of space required by the filter is substantially reduced.
    Type: Grant
    Filed: June 14, 1974
    Date of Patent: February 24, 1976
    Assignee: General Instrument Corporation
    Inventors: John Chesney, Chester R. Kruczek