Patent ID: 7642848

Claim:
A variable gain amplifying apparatus which is connected to a level detection circuit detecting the level of a receive signal in the rear of said variable gain amplifying apparatus and is controlled by a control circuit switching the gain of said variable gain amplifying apparatus, wherein said variable gain amplifying apparatus comprising: an amplifier; switching elements connected in parallel to said amplifier; and a phase shifter connected in series to said amplifier, said amplifier and said phase shifter directly connected between input terminals and output terminals, said phase shifter comprised of multi-stage circuits using passive elements, an impedance of said passive element monotonically increasing or monotonically decreasing from an input port of said phase shifter to an output port of said phase shifter, wherein said switching element is enabled if the level of an input signal or the level of an output signal is higher than a predetermined level, and said switching element is disabled if the level of said input signal or the level of said output signal is equal to or lower than said predetermined level, said amplifier and said phase shifter do not operate when said switching element is enabled by connecting said switching element in a closed circuit, the closed circuit in parallel with said amplifier and said phase shifter, and said amplifier and said phase shifter operate when said switching element is disabled, and the amount of phase shift generated when said input signal is passed through said amplifier and said phase shifter is substantially equal to the amount of phase shift generated when said input signal is passed through said switching element, and wherein said variable gain amplifying apparatus is switched to a low gain state if the level detected by said level detection circuit is higher than a predetermined level, and said variable gain amplifying apparatus is switched to a high gain state if the level detected by said level detection circuit is equal to or lower than said predetermined level.