Semiconductor integrated circuit with PLL circuit

Abstract

In a PLL circuit including an oscillator, a phase comparator, a charge pump circuit, and a loop filter, without providing a plurality of capacitative elements, that is, without increasing the occupied area so much, the characteristics of the PLL circuit can be adjusted according to manufacture variations in a resistive element and a capacitative element, and a loop filter can be formed on a chip. A resistive element and a capacitative element of a loop filter are formed on a semiconductor chip. As the resistive element, a plurality of elements having different resistance values are provided and switched by a switch, thereby enabling the resistance value to be adjusted. Current in a charge pump circuit is also made adjustable, and the current of the charge pump circuit is adjusted according to switching among the resistance values of the resistive elements.

1 .- 11 . (canceled)  
   
   
       12 . A radio communication system, comprising: 
 an antenna for transmitting and receiving signal electric waves;    a switch which is coupled to the antenna for switching transmission and reception;    a high-frequency power amplifier which is coupled to the switch for amplifying a transmission signal;    a radio-frequency IC which is coupled to the switch and the high-frequency power amplifier for demodulating a reception signal provided from the switch and modulating the transmission signal to be supplied to the high-frequency power amplifier and switch; and    a baseband circuit which is coupled to the radio-frequency IC for converting transmission data to I and Q signals and controlling the radio-frequency IC,    the radio-frequency IC formed on a semiconductor chip comprising:    a voltage-controlled oscillator which generates an oscillation signal;    a variable frequency divider which divides a frequency of the oscillation signal;    a reference oscillator which generates a reference oscillation signal;    a fixed frequency divider which divides a frequency of the reference oscillation signal;    a phase comparator which compares a phase of the oscillation signal divided by the variable frequency divider with a phase of the reference oscillation signal divided by the fixed frequency divider and generates a signal in accordance with a phase difference thereof;    a charge pump circuit which generates a charge current or discharge current according to the signal; and    a loop filter which provides a voltage to the voltage-controlled oscillator for controlling the frequency of the oscillation signal, the voltage being generated by smoothing the charge current or discharge current by the loop filter;    wherein a first resistive element and a first capacitive element which is included in the loop filter are formed on the semiconductor chip, the first resistive element is constructed by a plurality of resistive elements having different resistance values, and any of the plurality of elements is selectively connected,    wherein the charge pump circuit comprises a second resistive element which is constructed by a plurality of resistive elements having different resistance values, and the change in the charge current or discharge current is performed by selecting any of the plurality of resistive elements of the second resistive element, and    wherein the radio-frequency IC further comprises a correcting circuit for changing the charge current or discharge current in accordance with the selection of the second resistive element.    
   
   
       13 . A radio communication system according to  claim 12 , 
 wherein when the first resistive element having a small resistance value is selected in the loop filter, the second resistive element having a small resistance value is selected in the charge pump circuit, and when the first resistive element having a large resistance value is selected in the loop filter, the second resistive element having a large resistance value is selected in the charge pump circuit.    
   
   
       14 . A radio communication system according to  claim 13 , the radio-frequency IC further comprising a manufacture variation detector, 
 the manufacture variation detector including a current circuit that includes a third resistive element and outputs a current according to a resistance value of the third resistive element, a second capacitive element charged by the current circuit, and a voltage comparator which compares a charge voltage of the second capacitive element with a reference potential,    wherein selection of the first resistive element and the second resistive element is determined in accordance with a result of detection of a manufacture variation from a change in the charge voltage detected by the manufacture variation detector.    
   
   
       15 . A radio communication system according to  claim 14 , 
 wherein the loop filter is a second-order filter, and    wherein the first resistive element and the first capacitive element construct a first-order filter circuit.