FM modulator
AssigneeSony Corporation
InventorsKensaku Abe, Yoshihiro Sugimoto, Nobuo Kobayashi, Kazuhisa Kito
Life of this patent
Estimating the term…
Abstract
The signal source of the reference frequency of a PLL 20 is composed of a VCO 24. A VCO 14 is provided. A first audio signal (L+R) is supplied to the VCO 24 so as to control its oscillation frequency f24. A second audio signal (L−R) is supplied to the VCO 14, so that an FM signal SSUB is formed whose occupied frequency band is outside the band of the first audio signal (L+R). This FM signal SSUB is supplied to an adder 26, hereby added to a phase comparison output that is supplied to a VCO 21 from a low-pass filter, and then supplied to the VCO 21.
Claims3
A frequency modulation circuit, comprising:
- a first VCO;
- a frequency divider circuit for dividing an oscillation signal generated by said first VCO and for outputting a divided signal;
- an oscillation circuit for outputting an oscillation signal having a reference frequency;
- a phase comparison circuit for comparing phases of said divided signal output from said frequency divider circuit and said oscillation signal output from said oscillation circuit and for outputting a phase comparison output;
- and
- a low-pass filter for taking a direct-current voltage, having a level that corresponds to a phase difference between said divided signal and said oscillation signal, out of the phase comparison output of phase comparison circuit, and for outputting said direct-current voltage, wherein
- said direct-current voltage output from said low-pass filter is supplied to said first VCO as a control signal for its oscillation frequency, so that a PLL is composed;
- said oscillation circuit is composed of a second VCO;
- a first audio signal is supplied to said second VCO and an oscillation frequency thereof is controlled thereby;
- a sub-carrier signal is modulated by a second audio signal, so that a modulated signal is formed having a frequency band outside a frequency band of said first audio signal;
- and
- said modulated signal is added to said direct-current voltage output from said low-pass filter, and an obtained result is supplied to said first VCO.
Dependencies are inferred from the claim text.