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    MODIFIED WIEN BRIDGE OSCILLATOR
    1.
    发明专利
    MODIFIED WIEN BRIDGE OSCILLATOR 未知

    公开(公告)号：CA573236A

    公开(公告)日：1959-03-31

    申请号：CA573236D

    Applicant: HEWLETT PACKARD CO

    Inventor： OLIVER BERNARD M

    IPC: H03B5/22 ,  H03B5/28

    Abstract: 812,282. Valve oscillator and amplifier circuits. HEWLETT-PACKARD CO. Oct. 7, 1955, No. 28664/55. Class 40 (6). A valve oscillator circuit comprises a balanced amplifier having an input stage and a cathode follower output stage, a plurality of feedback circuits from the output to the input and a further feedback circuit providing positive feedback to reduce the output impedance of the amplifier. Fig. 1 shows an oscillator comprising a push-pull amplifier having a Wien bridge 11, 12, connected in feedback paths between the cathodes of the output valves and the grids of the input valves. The network 11 provides positive feedback and the network 12 negative feedback, a temperature-sensitive resistive element 50 being provided to control the amplitude of oscillation. The output is derived through a transformer 43 and a bridged-T attenuating network 45. The amplifier is provided with D.C. coupling between the anodes of the input valves and the control and screen grids of the output valve and positive feedback is provided from the anode of each output valve to the grid of the other valve through paths 35 and 36. This feedback is such that variations in the cathode impedance of the output valves due to changes in the load are offset by the consequent increase in gain of the output valves due to the positive feedback. The output impedance of the circuit is thus substantially zero and no change occurs in the feedback through the networks 11 and 12 as the load varies. Capacitors 41 and 42 from the anodes of the output valve to earth reduce the gain of the amplifier at high frequencies and a capacitance shunted resistance network 29, 30 reduces the gain at low frequencies and D.C. In an alternative amplifier, Fig. 3, the positive feedback for reducing the output impedance is provided between anodes and cathodes of the output valves. Resistors 64, 65, 67 and 68 are equal and the feedback is therefore such that a change in cathode voltage on one valve due to a change in output load are offset by an equal and opposite change at the anode of the opposite valve so that the potential at the junctions of the resistors and thus the feedback through the Wien bridge network remains unchanged.

    Television synchronizing system
    6.
    发明授权
    Television synchronizing system 失效
    电视同步系统

    公开(公告)号：US3567860A

    公开(公告)日：1971-03-02

    申请号：US3567860D

    申请日：1968-03-07

    Applicant: HEWLETT PACKARD CO

    Inventor： OLIVER BERNARD M ,  MONNIER RICHARD E ,  JUSTICE GREGORY

    IPC: H04N5/10 ,  H04N5/12

    CPC classification number: H04N5/10 ,  H04N5/126

    Abstract: A sync stripper removes the picture signal from the composite video input signal leaving a composite synchronizing signal that includes horizontal and vertical sync pulses. An oscillator produces a periodic timing signal having a repetition rate equal to twice that of the horizontal sync pulses. This timing signal is supplied to a binary scaler to produce a synchronizing signal for periodically triggering a horizontal deflection circuit at a repetition rate equal to that of the horizontal sync pulses. A feedback circuit, responsive to this synchronizing signal and to the composite synchronizing signal, phase locks the oscillator to the composite synchronizing signal and maintains the repetition rate of the oscillator at twice that of the horizontal sync pulses. The timing signal is also supplied to a gate that is periodically enabled in response to the vertical sync pulses to provide a synchronizing signal for periodically triggering a vertical deflection circuit at a repetition rate equal to that of the vertical sync pulses.

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