Frequency multiplier and semiconductor integrated circuit

Abstract

A frequency multiplication circuit with simple structure capable of surely removing unwanted higher harmonics. Inside the oscillation circuit 14a, cascade-connected three stages of 2-multiplication circuits 2 are provided. Since an 8-multiplied local oscillation signal is generated by supplying the source oscillation signal of the crystal oscillator to the 2-multiplication circuit 2 of the first stage, even when a source oscillation frequency is low, the local oscillation signal of a sufficiently high frequency can be generated. By providing a filter circuit 31 between the stages of the frequency multiplication circuit 2, a fixed phase shift quantity generated by a limiter amplifier 26 of the 90 deg. phase shift circuit 21a can be canceled by resistors R6-R8 inserted to the filter circuit 31, so that generation of unwanted higher harmonics is surely suppressed.

Description

Technical field

[0001] The present invention relates to a frequency multiplier circuit for generating local oscillator signals used in superheterodyne receivers and the like. Background technique

[0002] Recently, many systems have been proposed that transmit and receive weak radio waves and perform various processing in a non-contact manner. For example, a key-less entry system is a system that uses a receiving circuit on the side of the vehicle to receive weak radio waves emitted by a transmitting circuit embedded in the car key to open and close the door.

[0003] Figure 15 The block diagram shows the general structure of this existing weak radio wave transmitting and receiving system. Figure 15 The system is roughly divided into a transmitter 51 and a receiver 52. The transmitter 51 has a transmitting circuit 53 and an antenna 54. The transmitter 51 uses 315 MHz as the carrier frequency to transmit AM modulated (amplitude modulation) or FM modulated (frequency modulation)...

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