| 摘要 |
PURPOSE: A gain adjusting circuit for an RF(Radio Frequency) receiving unit by a single control signal is provided to generate a control signal for an LNA(Low Noise Amplifier) on/off switch and a control signal for an IF(Intermediate Frequency) automatic gain adjustment. CONSTITUTION: An operational amplifier(70) receives a gain control signal at its plus terminal from an MSM(Mobile Station Modem)(40), and receives the gain control signal at its minus terminal through the first and second diodes(D1,D2) connected in series. The first resistor(R1) connects to the minus terminal of the operational amplifier(70), and is grounded. An LNA switch unit(80) receives an output voltage of the operational amplifier(70). A subtracting unit(50) receives the output voltage of the operational amplifier(70) through the second resistor(R2) and receives the gain control signal from the MSM(40). The third resistor(R3) divides the voltage of the second resistor(R2) inputted to the subtracting unit(50) through the second resistor(R2). An IF automatic gain control unit(60) receives the output signal of the subtracting unit(50).
|
