Patent ID: 7218903

Claim:
A squelch detecting circuit comprising: a differential amplification circuit that amplifies differential input signals to output an amplified signal; a gain proportion circuit that supplies a potential proportional to said amplified signal; a potential holding circuit that holds said potential supplied from said gain proportion circuit; and a comparator circuit that compares said potential held by said potential holding circuit and a reference potential to output a detect signal, wherein said differential amplification circuit comprises a first operational amplifier that amplifies said differential input signals to output a single-end amplified signal, said gain proportion circuit comprises an n-type transistor that receives said single-end amplified signal at its control electrode and supplies a potential from its first current electrode to said potential holding circuit, said potential holding circuit comprises a first current source having its one terminal connected to said first current electrode of said n-type transistor and the other terminal connected to GND, and a first capacitance having its one terminal connected to said first current electrode of said n-type transistor and to said first current source and having the other terminal connected to GND, and said comparator circuit comprises a second operational amplifier that receives said potential held by said potential holding circuit and said reference potential.