Patent ID: 7486942
Filing Date: 2009-02-03
Classification: H04B

Abstract:
1. A receiver comprising: a low-noise amplifier that amplifies a received signal to output an amplified signal; a local oscillator that oscillates a local oscillation signal having a frequency different from a frequency of the amplified signal; and a mixer portion that receives the amplified signal and the local oscillation signal to convert the amplified signal into an intermediate-frequency signal having a frequency different from the frequency of the amplified signal and then output the intermediate-frequency signal, wherein the mixer portion comprises: a first mixer that exhibits a closely linear input/output characteristic in a high-signal-strength range where the amplified signal has a high signal strength; a second mixer that operates with lower current consumption than the first mixer and that exhibits, in an ordinary-signal-strength range where the amplified signal has an ordinary signal strength, a linear input/output characteristic and, in the high-signal-strength range where the amplified signal has a signal strength higher than in the ordinary-signal-strength range, a less linear input/output characteristic than the first mixer; a mixer switching circuit that receives a switching signal to choose and actuate one of the first and second mixers; a signal strength detection portion that detects and outputs a signal strength of the intermediate-frequency signal; and a mixer switching control portion that receives the signal strength to calculate an electric-field strength of the received signal based on a sum of a gain of the low-noise amplifier and a gain of whichever of the first and second mixers is chosen and that then, according to the calculated electric-filed strength, feeds the switching signal to the mixer switching circuit, wherein the mixer switching control portion compares the calculated electric-field strength with a predetermined threshold value so that, if the electric-field strength is higher than the threshold value, it is determined that the amplified signal is in the strength range and the mixer switching control portion outputs a switching signal that instructs the first mixer to be chosen, and if the electric-field strength is lower than the threshold value, it is determined that the amplified signal is in the ordinary-signal-strength range and the mixer switching control portion outputs a switching signal that instructs the second mixer to be chosen.