JP2009182523A - Current source circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a current source circuit which is hard to be affected by variations in resistance due to a process. <P>SOLUTION: A current source circuit 100 includes a resistance value control circuit 101 including: a comparator 103 which receives drain voltages of MOS transistors Q6 and Q7 and outputs the comparison results between the received drain voltages to a control part 104; and the control part 104 which outputs a digital control signal based on the output of the comparator 103 and changes resistance values of variable resistances R1 and R2. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a current source circuit used for a VCO (Voltage control Oscillator) or the like.

  In general, in a VCO based on LC resonance, the resonance impedance greatly varies depending on the temperature. When the resonance impedance varies, the oscillation amplitude of the VCO varies. In this case, the phase noise characteristic that is important for the VCO is deteriorated.

  Therefore, by providing the VCO current source circuit with a temperature characteristic opposite to the temperature characteristic, the fluctuation of the resonant impedance due to the temperature change is canceled and the oscillation amplitude of the VCO is kept constant, thereby preventing the deterioration of the phase noise characteristic. ing.

FIG. 5 is a diagram showing a conventional example of a current source circuit used for a VCO.
A current source circuit 500 shown in FIG. 5 is a current source circuit including a current mirror circuit including transistors Q1, Q2, and Q3 and a current mirror circuit including transistors Q4 and Q5. The sources of the transistors Q1 to Q3 are connected to the power supply, the transistors Q1 to Q4 and Q2 to Q5 are connected to each other through the drain and the collector, and the emitters of the transistors Q4 and Q5 are grounded.

  In the current source circuit 500, a resistor R is connected to the emitter side of the transistor Q5 in order to provide temperature characteristics. Thereby, it is possible to have a temperature characteristic opposite to the temperature characteristic of the VCO connected to the current source circuit 500. However, there is a problem that it is easily affected by resistance variation due to the process.

Therefore, in general, the resistor R shown in FIG. 5 is externally attached so as not to be affected by the resistance variation due to the process.
However, if the resistor R is externally attached, it becomes easy to pick up noise from the terminals and external patterns. When the current source circuit 500 picks up noise, the noise flows into the VCO from the current source circuit 500, which causes a problem that the phase noise characteristics of the VCO are deteriorated.

  In relation to the above technique, Patent Document 1 discloses a time constant automatic adjustment circuit that detects an R error generated in an IC manufacturing process and automatically adjusts a variation in a constant caused by the R error using the detected value. Has been.

Japanese Patent Laid-Open No. 2004-228561 detects a variation in the resistance value of the semiconductor device internal resistance using the semiconductor device internal reference resistance and the semiconductor device external reference resistance, and automatically corrects the resistance value according to the amount of variation in the resistance value. An automatic resistance value variation correcting circuit is disclosed.
JP 04-340244 A JP 2001-203574 A

  The present invention has been made in view of the above-described problems, and a problem to be solved is to provide a current source circuit that is not easily affected by variations in resistance due to processes.

  In order to solve the above problems, the current source circuit is a current source circuit that supplies a constant current to a voltage controlled oscillation circuit using LC resonance, and has a temperature opposite to the temperature characteristic of the voltage controlled oscillation circuit. A current supply circuit having a first variable resistor as a current source circuit having characteristics, supplying a constant current to the voltage controlled oscillation circuit, a resistance value of an external resistor having desired temperature characteristics, and the first resistance A resistance value control circuit that changes the resistance value of the first variable resistor so that the resistance value of the variable resistor matches or substantially matches.

  According to this current source circuit, the resistance value control circuit adjusts the resistance value of the first variable resistor so that the resistance value of the external resistor and the resistance value of the first variable resistor match or substantially match. As a result, the temperature characteristic of the external resistance value can be given to the current source circuit. Therefore, even if resistance variation due to the process occurs in the first variable resistor, it is possible to make it less susceptible to the resistance variation.

  As described above, according to the present invention, it is possible to provide a current source circuit that is not easily affected by resistance variations due to processes.

Hereinafter, embodiments of the present invention will be described with reference to FIGS.
FIG. 1 is a diagram illustrating an embodiment of a current source circuit 100 according to an embodiment of the present invention.
A current source circuit 100 shown in FIG. 1 includes p-type MOS transistors Q1, Q2, and Q3, npn-type bipolar transistors Q4 and Q5, a resistor r, a variable resistor R1, and a resistance value that controls the resistance value of the variable resistor R1. And a control circuit 101. Note that the variable resistor R1 and the variable resistor R2 shown below have resistance values that give the current source circuit 100 a temperature characteristic opposite to the temperature characteristic of the VCO 105. Further, it is desirable that the variable resistors R1 and R2 are arranged adjacent to each other in order to make the tendency of variation due to the process the same.

  Here, MOS transistors Q1, Q2 and Q3 constitute a current mirror circuit. Further, between the MOS transistor Q1 and the bipolar transistor Q4, a drain and a collector are connected via a resistor r, and between the MOS transistor Q2 and the bipolar transistor Q5, a drain and a collector are directly connected. The sources of MOS transistors Q1, Q2 and Q3 are connected to the power supply, and the emitter of bipolar transistor Q4 is grounded. The emitter of the bipolar transistor Q5 is grounded via the variable resistor R1.

  The resistance value control circuit 101 includes a variable resistor R2, an external resistor R3, a p-type MOS transistor Q6 whose source is connected to the power source and whose drain is grounded via the variable resistor R2, and whose source is connected to the power source and whose drain is A p-type MOS transistor Q7 grounded via an external resistor R3, a comparator 102 for inputting the reference voltage Vref and the drain voltage of the MOS transistor Q7 and outputting the comparison result to the gates of the MOS transistors Q6 and Q7; The comparator 103 that inputs the drain voltages of the MOS transistors Q6 and Q7 and outputs the comparison result to the control unit 104, and the digital control signal (hereinafter referred to as “control signal”) according to the output of the comparator 103 are variable resistors. And a control unit 104 that outputs to R1 and R2 and changes both resistance values. That.

VCO 105 is a cross-coupled oscillation circuit including n-type MOS transistors Q10 to Q13, varicaps C1 and C2, and inductors L1 and L2.
Here, the MOS transistors Q10 and Q11 are current source circuits constituting a current mirror circuit. The drain of MOS transistor Q10 is connected to the drain of MOS transistor Q3. The drain of MOS transistor Q11 is connected to the sources of MOS transistors Q12 and Q13. The sources of MOS transistors Q10 and Q11 are grounded.

  On the other hand, MOS transistors Q12 and Q13 have their gates and drains connected to each other, and the drains of transistors Q12 and Q13 have one end of inductor L1 and the cathode of varicap C1, one end of inductor L2 and the cathode of varicap C2, respectively. Connected. The other ends of the inductors L1 and L2 are connected to the power source, and the anodes of the varicaps C1 and C2 are connected to the input terminal of the control voltage Vt.

  In the above configuration, the VCO 105 can change the oscillation frequency according to the control voltage Vt because the capacitors of the varicaps C1 and C2 change when the control voltage Vt is applied.

  The illustrated VCO 105 is a general VCO and will not be described in detail. The VCO connected to the current source circuit 100 according to the present embodiment is not limited to the illustrated VCO 105, and an effect similar to that of the present embodiment can be obtained as long as the VCO is based on LC resonance.

  When the reference voltage Vref is applied to the comparator 102 of the resistance value control circuit 101, the comparator 102 applies an output voltage to the gates of the MOS transistors Q6 and Q7 so that the drain voltage of the MOS transistor Q7 is equal to the reference voltage Vref. . As a result, the same current flows between the source and drain of both transistors.

  The comparator 103 compares the drain voltages of the MOS transistors Q6 and Q7 and outputs the comparison result to the control unit 104. In accordance with the output of the comparator 103, the control unit 104 generates a control signal so that both voltages match or substantially match, and outputs the control signal to the variable resistors R1 and R2 to output resistances of the variable resistors R1 and R2. Increase or decrease the value.

  At this time, for example, the control unit 104 may monitor the timing at which the output of the comparator 103 switches from 0 to 1, or from 1 to 0, and may determine that both voltages match or substantially match when the timing is detected. .

Here, generally, since the tendency of the resistance variation due to the process in the same cell is the same, the tendency of the resistances R1 and R2 is the same.
Therefore, the variable resistor R1 (R2) is adjusted to have the same resistance value as the external resistor R3 by the above-described operation. As a result, even when resistance variation due to the process occurs in the resistor R1, it is possible to give the current source circuit 100 a desired temperature characteristic without being affected by the variation.

  In addition, since the control unit 104 controls the variable resistors R1 and R2 with digital signals, even if noise flows into the resistance value control circuit 101 from an external terminal, an external pattern, or the like, the control unit 104 controls the variable resistors R1 and R2. It does not flow into R1 and R2.

  As a result, it is possible to prevent noise from an external terminal, an external pattern, etc. from being picked up and flowing into the VCO even if the resistor that gives the current source circuit 100 temperature characteristics is an external resistor. As a result, it is possible to prevent deterioration of the phase noise characteristics of the VCO connected to the current source circuit 100 due to the noise.

  In the above configuration, for example, the current source supply unit can be realized by the p-type MOS transistors Q1, Q2, and Q3, the npn-type bipolar transistors Q4 and Q5, the resistor r, and the variable resistor R1 shown in FIG. The resistance value control unit can be realized by the resistance value control circuit 101.

FIG. 2 is a diagram illustrating a configuration example of the variable resistors R1 and R2 according to the embodiment of the present invention. Since both resistors have the same configuration, the variable resistor R1 will be described below.
The variable resistor R1 shown in FIG. 2 includes resistors r1, r2, r3, r4, and r5 and switches SW1, SW2, SW3, and SW4. The resistors r1, r2, r3, r4, and r5 are connected in series, and the switches SW1, SW2, SW3, and SW4 are connected in parallel to the resistors r1, r2, r3, and r4, respectively.

  For example, n-type MOS transistors Qr1, Qr2, Qr3, and Qr4 may be used for the switches SW1, SW2, SW3, and SW4 as shown in FIG. In this case, resistors r1, r2, r3, and r4 are connected between the drain and source of the MOS transistors Qr1, Qr2, Qr3, and Qr4, respectively, and a control signal from the control unit 104 is sent to the gate of each transistor (for each bit). ) What is necessary is just to apply.

FIG. 3 is a flowchart for explaining the operation of the control unit 104 according to the present embodiment.
When the resistance value control circuit 101 starts operation, the control unit 104 proceeds to step S301.

In step S <b> 301, the control unit 104 reads the output signal of the comparator 103. Then, the process proceeds to step S302.
In step S302, the control unit 104 determines whether or not the output signal of the comparator 103 read in step S301 is zero. And when the said output signal is 0, the control part 104 transfers a process to step S303.

  In step S <b> 303, the control unit 104 increments a counter register (hereinafter referred to as “register”) included in the control unit 104 by one. Then, the process proceeds to step S301.

On the other hand, when the output signal is not 0 in step S302, the control unit 104 shifts the process to step S304.
In step S304, the control unit 104 stores the register value in a storage unit provided in the control unit 104. In step S305, the control unit 104 sets the value of the register in the bias circuit in which each bit is connected to the switches SW1 to SW4 illustrated in FIG. Thereby, ON / OFF of the switches SW1 to SW4 is switched according to the value of the register counter.

  For example, when the resistance values of the resistors r1 to r5 are in a relationship of r1 <r2 <r3 <r4 <r5, the first bit of the control signal (LSB (Least Significant Bit)) is applied to each of the switches SW1, SW2, SW3, and SW4. If the second bit, the third bit, and the fourth bit (MSB (Most Significant Bit)) are assigned, the resistance value of the variable resistor R1 can be increased as the count value increases.

  In step S302, it is determined whether or not the output signal of the comparator 103 matches 0. For example, whether or not the output signal matches or substantially matches 0 (for example, a range of 0 ± 0.1). May be determined.

  In this embodiment, the case where the data length of the control signal is 4 bits has been described. However, it is natural that the data length is not limited to 4 bits. For example, the data length of the control signal may be appropriately determined according to the number of resistors constituting the variable resistance value R1 (variable range of resistance value, variable resistance value unit).

  As described above, in the current source circuit 100 according to the present embodiment, the resistance value of the variable resistor R2 and the resistance value of the external resistor R3 that have the same resistance variation tendency due to the process match (or substantially match). Thus, since the resistance control circuit 101 adjusts the variable resistor R2, it is possible to prevent the current source circuit 100 from being affected by the variation even if the variable resistance value R1 has a resistance variation due to the process. . As a result, the current source circuit 100 can have desired temperature characteristics.

  Further, since the control signal from the control unit 104 to the variable resistance value R1 is a digital signal, for example, even when noise is picked up from an external terminal or an external pattern to which the external resistance R3 is connected, the variable resistance R1 There is no inflow. As a result, as shown in FIG. 4, it is possible to prevent noise from an external terminal and an external pattern from being picked up and flowing into the VCO from the current source circuit 100 to deteriorate the phase noise characteristics of the VCO.

  Further, since a digital signal is used as a control signal from the control unit 104 to the variable resistance value R1, even if the resistance value control circuit 101 is added to the current source circuit 100, noise in the current source circuit 100 is increased. Can be prevented.

  In the characteristic graph shown in FIG. 4, the horizontal axis represents the variation rate of the resistors constituting the current source circuit 100, and the vertical axis represents the phase noise when the current source circuit 100 is used as a VCO current source. . The current source circuit 100 according to the present embodiment keeps the resistance variation due to the process constant (the variation rate is kept at 5% in FIG. 4), and even when an external resistor is used, it is the same as when an internal resistor is used. It shows that it becomes phase noise (arrow in the figure).

  Therefore, by using the current source circuit 100 as a current source of the VCO, the amplitude value of the VCO can be kept constant, so that the phase noise characteristics can be maintained in an optimum state.

It is a figure which shows the Example of the current source circuit which concerns on the Example of this invention. It is a figure which shows the structural example of variable resistance R1 and R2 which concern on the Example of this invention. It is a flowchart explaining operation | movement of the control part which concerns on a present Example. It is a figure explaining the effect at the time of using the current source circuit concerning a present Example for VCO. It is a figure which shows the prior art example of the current source circuit used for VCO.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Current source circuit 101 ... Resistance value control circuit 102 ... Comparator 103 ... Comparator 104 ... Control part 105 ... VCO

Claims (4)

A current source circuit for supplying a constant current to a voltage controlled oscillation circuit using LC resonance,
A current supply circuit having a first variable resistor having a temperature characteristic opposite to the temperature characteristic of the voltage controlled oscillation circuit, and supplying a constant current to the voltage controlled oscillation circuit;
A resistance value control circuit for controlling the resistance value of the second variable resistor so that the resistance value of the external resistor having a desired temperature characteristic and the resistance value of the second variable resistor match or substantially match;
A current source circuit comprising: The resistance value control circuit includes a second variable resistor having the same configuration as that of the first variable resistor, and the resistance value of the second variable resistor and the resistance value of the external resistor match or substantially match. So that the resistance value of the second variable resistor is controlled,
The current source circuit according to claim 1. The resistance values of the first and second variable resistors are controlled according to a digital control signal generated by the resistance value control unit.
The current source circuit according to claim 1. A voltage controlled oscillation circuit using LC resonance,
A current supply circuit having a first variable resistor having a temperature characteristic opposite to the temperature characteristic of the voltage controlled oscillation circuit, and supplying a constant current to the voltage controlled oscillation circuit;
A resistance value control circuit for controlling the resistance value of the first variable resistor so that the resistance value of the external resistor having a desired temperature characteristic matches or substantially matches the resistance value of the second variable resistor;
A voltage controlled oscillation circuit using a current source circuit comprising:

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