| 摘要 |
PURPOSE:To evade saturation with simple circuit constitution and to stably and securely expands the AGC range of the whole device by providing feedback independently to a radio frequency processing means and an intermediate frequency processing means by using an RSSI signal and adjusting a gain. CONSTITUTION:A variable gain type is applied as a preamplifier(LNA) 3 and/or a 1st mixer 5, and a differential amplifier 25 of operational amplifier constitution is provided. The differential amplifier 25 inputs the RSSI signal from the intermediate frequency amplifier 11 and a limiter 13 at its inverted input terminal and a reference voltage Vrer at its uninverted input terminal. Then a signal of the difference of the RSSI signal, showing the current received signal level, from the reference voltage Vref is obtained and supplied as a gain variation signal to the LNA3 and/or mixer 5. The amplifler 25, therefore, constitutes the principal part of the gain varying means. |
