Oscillator circuit and L load differential circuit achieving a wide oscillation frequency range and low phase noise characteristics

Abstract

An oscillator circuit is formed of a differential LC resonant circuit formed of an L load differential circuit including inductance-variable portions and a capacitor element, and a positive feedback circuit formed of N-channel MOS transistors. The inductance-variable portion is configured to vary the inductance by selecting a plurality of switch circuits arranged between a plurality of arbitrary positions on a spiral interconnection layer and the input/output terminal, and thereby can control an oscillation frequency. The inductance-variable portions form an inductor pair when the switch circuit among the switch circuits coupled between the first input/output terminals is turned on together with the switch circuit.

What is claimed is:  
     
         1 . An oscillator circuit for performing oscillation by positive feedback of an LC resonant circuit, wherein 
 said LC resonant circuit includes a parallel resonant circuit formed of an inductance-variable portion allowing variation of an inductance by a switch circuit and a capacitor element.    
     
     
         2 . The oscillator circuit according to  claim 1 , wherein 
 said inductance-variable portion includes    first and second input/output terminals,    a spiral interconnection layer starting from said first input/output terminal, and formed on a semiconductor substrate with an interlayer insulating film therebetween, and    a plurality of switch circuits having first terminals connected to arbitrary positions on said interconnection layer, and having second terminals commonly connected to said second input/output terminal, and    when one of said plurality of switch circuits is turned on, the position on said interconnection layer connected to said turned-on switch circuit is electrically coupled to said second input/output terminal.    
     
     
         3 . The oscillator circuit according to  claim 2 , wherein 
 said inductance-variable portion further includes a plurality of second switch circuits each having a first terminal connected to the first terminal of one of said plurality of switch circuits, and having a second terminal connected to the first terminal of another one of said plurality of switch circuits, and    when one of said plurality of switch circuits and one of said plurality of second switch circuits are turned on, the position on said interconnection layer connected to said turned-on switch circuit is electrically coupled to said second input/output terminal.    
     
     
         4 . The oscillator circuit according to  claim 1 , wherein 
 said inductance-variable portion includes    first and second input/output terminals,    a plurality of spiral interconnection layers starting from said first input/output terminal, and formed on a semiconductor substrate with an interlayer insulating film therebetween, and    said plurality of switch circuits connected between trailing ends of said plurality of interconnection layers and said second input/output terminal, respectively, and    when one of said plurality of switch circuits is turned on, the trailing end of said interconnection layer included in said plurality of interconnection layers and connected to said turned-on switch circuit is electrically coupled to said second input/output terminal.    
     
     
         5 . The oscillator circuit according to  claim 3 , wherein 
 said switch circuit includes a transistor element to be turned on/off in accordance with a voltage level of a control voltage.    
     
     
         6 . The oscillator circuit according to  claim 1 , wherein 
 said capacitor element in said LC resonant circuit has a variable capacitance value.    
     
     
         7 . An oscillator circuit, comprising: 
 a pair of transistors cross-coupled to each other; and    an LC resonant circuit of a differential type coupled to said pair of transistors in a feedback manner; wherein    said LC resonant circuit includes    first and second inductance-variable portions including first and second input/output terminals, said second input/output terminals being commonly connected to a fixed node, and said first and second inductance-variable portions being capable of varying inductances, and    a first switch circuit coupled between the first input/output terminals of said first and second inductance-variable portions,    each of said first and second inductance-variable portions has    a spiral interconnection layer starting from said first input/output terminal and formed on a semiconductor substrate with an interlayer insulating film therebetween, and    a plurality of second switch circuits having first terminals connected to arbitrary positions on said interconnection layer and second terminals commonly connected to said second input/output terminal, respectively,    when one of said plurality of second switch circuits is turned on, the position on said interconnection layer connected to said turned-on second switch circuit is electrically coupled to said second input/output terminal, and    when said first switch circuit is turned on in response to the turn-on of said second switch circuit, said first switch circuit electrically couples said first and second inductance-variable portions.    
     
     
         8 . An oscillator circuit, comprising: 
 a pair of transistors cross-coupled to each other; and    an LC resonant circuit of a differential type coupled to said pair of transistors in a feedback manner; wherein    said LC resonant circuit includes    first and second inductance-variable portions including first and second input/output terminals, said second input/output terminals being commonly connected to a fixed node, and said first and second inductance-variable portions being capable of varying inductances, and    a first switch circuit coupled between the first input/output terminals of said first and second inductance-variable portions,    each of said first and second inductance-variable portions has    a plurality of spiral interconnection layers starting from said first input/output terminal and formed on a semiconductor substrate with an interlayer insulating film therebetween, and    a plurality of second switch circuits coupled between trailing ends of said plurality of interconnection layers and said second input/output terminal, respectively,    when one of said plurality of second switch circuits is turned on, the trailing end of said interconnection layer included in said plurality of interconnection layers and connected to said turned-on second switch circuit is electrically coupled to said second input/output terminal, and    when said first switch circuit is turned on in response to the turn-on of said second switch circuit, said first switch circuit electrically couples said first and second inductance-variable portions.    
     
     
         9 . The oscillator circuit according to  claim 7 , wherein 
 said first and second inductance-variable portions form a differential inductor element.    
     
     
         10 . The oscillator circuit according to  claim 7 , wherein 
 each of said first and second switch circuits includes a transistor element to be turned on/off in accordance with a voltage level of a control voltage.    
     
     
         11 . The oscillator circuit according to  claim 7 , wherein 
 said capacitor element in said LC resonant circuit has a variable capacitance value.    
     
     
         12 . An L load differential circuit, comprising an inductor pair including first and second inductance-variable portions having second input/output terminals commonly connected to a fixed node and being capable of varying inductances, and a first switch circuit coupled between first input/output terminals of said first and second inductance-variable portions, wherein 
 each of said first and second inductance-variable portions has    a spiral interconnection layer starting from said first input/output terminal and formed on a semiconductor substrate with an interlayer insulating film therebetween, and    a plurality of second switch circuits having first terminals connected to arbitrary positions on said interconnection layer and second terminals commonly connected to said second input/output terminal, respectively,    when one of said plurality of second switch circuits is turned on, the position on said interconnection layer connected to said turned-on second switch circuit is electrically coupled to said second input/output terminal, and    when said first switch circuit is turned on in response to the turn-on of said second switch circuit, said first switch circuit electrically couples said first and second inductance-variable portions.    
     
     
         13 . An L load differential circuit, comprising an inductor pair including first and second inductance-variable portions having second input/output terminals commonly connected to a fixed node and being capable of varying inductances, and a first switch circuit coupled between first input/output terminals of said first and second inductance-variable portions, wherein 
 each of said first and second inductance-variable portions has    a plurality of spiral interconnection layers starting from said first input/output terminal and formed on a semiconductor substrate with an interlayer insulating film therebetween, and    a plurality of second switch circuits coupled between trailing ends of said plurality of interconnection layers and said second input/output terminal, respectively,    when one of said plurality of second switch circuits is turned on, the trailing end of said interconnection layer included in said plurality of interconnection layers and connected to said turned-on second switch circuit is electrically coupled to said second input/output terminal, and    when said first switch circuit is turned on in response to said turn-on of said second switch circuit, said first switch circuit electrically couples said first and second inductance-variable portions.