Semiconductor device, radio communication device, and control method for radio communication device

Abstract

A semiconductor device includes a receiving unit that receives a radio signal, which includes a quadrature conversion circuit and an analog-to-digital converter, a received signal strength measurement unit, a threshold comparison unit, a demodulation unit, and a threshold setting unit. The analog-to-digital converter converts a received radio signal from the quadrature conversion circuit to a received signal. The received signal strength measurement unit measures the received signal and outputs a received signal strength. The threshold comparison unit compares the received signal strength with a threshold and outputs a comparison result. The demodulation unit demodulates the received signal based on the comparison result. The threshold setting unit sets the threshold according to the received signal strength.

What is claimed is: 
     
         1 . A semiconductor device, comprising:
 a receiving unit that receives a radio signal, which includes a quadrature conversion circuit and an analog-to-digital converter;   a received signal strength measurement unit;   a threshold comparison unit;   a demodulation unit; and   a threshold setting unit,   wherein the analog-to-digital converter converts a received radio signal from the quadrature conversion circuit to a received signal,   wherein the received signal strength measurement unit measures the received signal and outputs a received signal strength,   wherein the threshold comparison unit compares the received signal strength with a threshold and outputs a comparison result,   wherein the demodulation unit demodulates the received signal based on the comparison result, and   wherein the threshold setting unit sets the threshold according to the received signal strength.   
     
     
         2 . The semiconductor device according to  claim 1 , wherein the threshold setting unit sets the threshold based on a distance corresponding to the received signal strength. 
     
     
         3 . The semiconductor device according to  claim 1 , further comprising a storage unit that stores a threshold table for associating the received signal strength with the threshold,
 wherein the threshold setting unit refers to the threshold table and sets the threshold corresponding to the received signal strength.   
     
     
         4 . The semiconductor device according to  claim 1 , wherein, when there is no error in a demodulation result, the threshold setting unit sets the threshold according to the received signal strength. 
     
     
         5 . The semiconductor device according to  claim 1 , wherein the threshold setting unit sets the threshold based on a result of a comparison between a setting determination threshold and the received signal strength, the setting determination threshold being used for setting the threshold. 
     
     
         6 . The semiconductor device according to  claim 5 , wherein the threshold setting unit sets a first threshold to the threshold when the received signal strength is smaller than the setting determination threshold and sets a second threshold to the threshold when the received signal strength is larger than the setting determination threshold, the second threshold being larger than the first threshold. 
     
     
         7 . The semiconductor device according to  claim 1 , wherein the threshold setting unit sets the threshold based on a received signal state corresponding to the received signal strength. 
     
     
         8 . The semiconductor device according to  claim 7 , wherein, when the received signal strength meets a state transition condition corresponding to the received signal state, the threshold setting unit changes its state to the received signal state and sets the threshold according to the changed received signal state. 
     
     
         9 . The semiconductor device according to  claim 8 , wherein the state transition condition includes a condition for determining a number of receptions of radio signals having a predetermined received signal strength. 
     
     
         10 . The semiconductor device according to  claim 8 , wherein, when a first state transition condition is met, the threshold setting unit changes its state from a first received signal state to a second received signal state, and
 wherein, when a second state transition condition is met, the threshold setting unit changes its state from the second received signal state to the first received signal state, the second state transition condition being different from the first state transition condition.   
     
     
         11 . The semiconductor device according to  claim 1 , further comprising a reception gain setting unit that sets a reception gain of the receiving unit according to the measured received signal strength. 
     
     
         12 . The semiconductor device according to  claim 1 , further comprising:
 a transmitting unit that transmits a radio signal according to transmission data; and   a transmission power setting unit that sets transmission power of the transmitting unit according to the measured received signal strength.