JP4549979B2 - Voltage controlled oscillator - Google Patents

Description

  The present invention relates to a voltage-controlled oscillator (VCO) used in a wireless transmission / reception apparatus or the like.

The voltage controlled oscillator is an oscillator that can change the frequency of an oscillation signal by a control voltage. For example, an LC resonance type voltage controlled oscillator is often used for phase correction of a PLL (Phase Locked Loop) circuit in a wireless transmission / reception apparatus.
FIG. 4 shows a conventional example of an LC resonance type voltage controlled oscillator. The LC resonance type voltage controlled oscillator VCO has a main body unit MU and a bias unit BU. The main body MU includes inductors L1 and L2, capacitors C1 and C2, and nMOS transistors T1 and T2. One end of the inductor L1 and one end of the inductor L2 are connected to the power supply line VDD. One end of the capacitor C1 and one end of the capacitor C2 are connected to the ground line VSS. The drain of the nMOS transistor T1, the gate of the nMOS transistor T2, the other end of the inductor L1, the other end of the capacitor C1, and the terminal P1 are connected to each other. The drain of the nMOS transistor T2, the gate of the nMOS transistor T1, the other end of the inductor L2, the other end of the capacitor C2, and the terminal P2 are connected to each other. The source of the nMOS transistor T1 and the source of the nMOS transistor T2 are connected to the node ND. The capacitor value of the capacitor C1 is variable according to the control voltage received via the terminal P3. Similarly, the capacitor value of capacitor C2 is variable according to the control voltage received via terminal P4.

  The bias unit BU is configured using a current mirror circuit including a current source CS and nMOS transistors TB1 and TB2. One end of the current source CS is connected to the power supply line VDD. The other end of the current source CS, the drain of the nMOS transistor TB1, the gate of the nMOS transistor TB1, and the gate of the nMOS transistor TB2 are connected to each other. The source of the nMOS transistor TB1 and the source of the nMOS transistor TB2 are connected to the ground line VSS. The drain of the nMOS transistor TB2 is connected to the node ND of the main body MU. With such a configuration, a bias current proportional to the transistor size of the current source CS is supplied to the main body MU (node ND) via the nMOS transistor TB2. A voltage controlled oscillator in which a bias current is supplied to the main body by the bias unit having such a configuration is disclosed in Non-Patent Document 1, for example.

  In the voltage controlled oscillator VCO having the above-described configuration, the cross-coupled nMOS transistors T1 and T2 generate negative resistance and continue stable LC oscillation. The nMOS transistor TB2 functions as a current source for supplying a bias current to the main body MU, and maintains stable oscillation characteristics against fluctuations in the power supply voltage. Accordingly, differential signals (oscillation signals) whose phases are shifted by 180 ° are stably output from the terminals P1 and P2. Further, the frequency of the differential signal output from the terminals P1 and P2 can be controlled by changing the capacitor values of the capacitors C1 and C2 by the control voltage applied to the terminals P3 and P4.

  By the way, in the voltage controlled oscillator VCO having the above-described configuration, a large current is applied to the nMOS transistor TB1 in order to start up upon power-on and to make a fast transition to a stable state (steady state) of the oscillation signal frequency and amplitude. Need to flow. In addition, even after the transition to the steady state, in order to supply a bias voltage to the gate of the nMOS transistor TB2, it is necessary to continue flowing a current to the nMOS transistor TB1. For this reason, when the voltage controlled oscillator VCO is in a steady state, noise generated in the nMOS transistor TB1 is transmitted to the gate of the nMOS transistor TB2, and a bias current accompanied by noise is supplied to the main body MU. The phase noise of the VCO will increase.

Noise generated in the MOS transistor includes thermal noise and flicker noise. Flicker noise is dominant in the low frequency region, and thermal noise is dominant in the high frequency region (see, for example, Non-Patent Document 2). Thermal noise and flicker noise can be reduced by increasing the gate width of the MOS transistor. Therefore, in the voltage controlled oscillator VCO, the noise generated in the nMOS transistor TB1 can be reduced by increasing the gate width of the nMOS transistor TB1, but there is a problem that the current consumption increases. In addition, if the currents of the current source CS and the nMOS transistor TB1 are reduced without considering the phase noise in the steady state of the voltage controlled oscillator VCO, the time required for transition to the steady state increases. Low power consumption cannot be achieved at the same time.
N.Itoh, K. Hirashiki, T. Terada, M. Kikuta, S. Ishizuka, T. Koto, T. Suzuki and H. Aoki, "High Sensitivity 900-MHz ISM Band Transceiver," IEICE Trans. Fundamentals, Vol. E88-A, No.2, pp.498-506, February 2005. Kenji Taniguchi, "Introduction to CMOS Analog Circuits," pp.96-98, CQ Publishing, 2005.

  As described above, in the conventional voltage controlled oscillator, in order to make a transition to the steady state at a high speed and to continue supplying the bias current with low phase noise in the steady state, the bias is applied in both the startup state and the steady state. A large current must flow through the part. For this reason, the conventional voltage controlled oscillator has not been able to satisfy all of the high-speed startability, low phase noise, and low power consumption.

  The present invention has been made in view of such conventional problems, and provides a voltage-controlled oscillator capable of satisfying all of high-speed startability, low phase noise characteristics, and low power consumption. Objective.

The voltage controlled oscillator according to claim 1 is a main body for generating an oscillation signal having a desired frequency according to a control voltage, a current source, a first transistor connected in series to the current source, and a current mirror connection to the first transistor. is, a voltage controlled oscillator and a bias section having a second transistor for supplying a bias current to the body portion, the bias unit includes a switching circuit connected between the control terminals of the first and second transistors, And a capacitor connected between the control terminal of the second transistor and the ground line , and the current source performs a current supply operation to the first transistor when the voltage controlled oscillator is in a starting state, and the current source operates when the voltage controlled oscillator is in a steady state. The current supply operation to one transistor is stopped, and the switch circuit is turned on when the voltage controlled oscillator is in the starting state, and the voltage controlled oscillator Characterized in that it off at the time.

According to another aspect of the present invention, there is provided a voltage-controlled oscillator that generates an oscillation signal having a desired frequency according to a control voltage, a current source, a first transistor connected in series to the current source, and a current mirror connection to the first transistor. And a bias control unit having a second transistor for supplying a bias current to the main body, and the bias unit is connected between the control terminals of the first and second transistors and functions as a resistance element. And a capacitor connected between the control terminal of the second transistor and the ground line , and the current source performs a current supply operation to the first transistor with the first supply capability when the voltage controlled oscillator is in an activated state. In the steady state of the voltage controlled oscillator, the current supply operation for the first transistor is performed with the second supply capability smaller than the first supply capability. Latch circuit is turned on at first resistance value at start state of the voltage controlled oscillator, characterized in that on at higher than the first resistance value second resistance value when the steady state of the voltage controlled oscillator.

  The voltage controlled oscillator according to the present invention can satisfy all three important characteristics of fast start-up, low phase noise, and low power consumption.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a first embodiment of the present invention. FIG. 2 shows an example of the transmission gate of FIG. In describing the first embodiment of the present invention, the same elements as those described in the conventional example (FIG. 4) are denoted by the same reference numerals, and detailed description thereof is omitted.
The LC resonance type voltage controlled oscillator VCOA is configured by replacing the bias unit BU with a bias unit BUA with respect to the voltage controlled oscillator VCO of FIG. The bias unit BUA is configured by replacing the bias unit BU of FIG. 4 by replacing the current source CS with a current source CSA and adding a transmission gate TGA, a capacitor CB, and a control circuit CTLA. One end of the transmission gate TGA is connected to the other end of the current source CSA, the drain of the nMOS transistor TB1, and the gate of the nMOS transistor TB1. The other end of the transmission gate TGA is connected to one end of the capacitor CB and the gate of the nMOS transistor TB2. The other end of the capacitor CB is connected to the ground line VSS.

  The current source CSA performs / stops the current supply operation for the nMOS transistor TB1 in accordance with an instruction from the control circuit CTLA. The transmission gate TGA is turned on / off according to an instruction from the control circuit CTLA. For example, as shown in FIG. 2, the transmission gate TGA is configured by a pMOS transistor SWP and an nMOS transistor SWN that receive a control signal supplied from the control circuit CTLA at the gate and are connected in parallel.

  The control circuit CTLA instructs the current source CSA to perform the current supply operation for the nMOS transistor TB1 and also instructs the transmission gate TGA to turn on as the voltage controlled oscillator VCOA is turned on. The control circuit CTLA instructs the current source CSA to stop the current supply operation with respect to the nMOS transistor TB1 and instructs the transmission gate TGA to transition to the off state in accordance with the transition of the voltage controlled oscillator VCOA to the steady state.

  In the voltage controlled oscillator VCOA having the above-described configuration, in the start-up state, a large current is supplied from the current source CSA to the nMOS transistor TB1, and the transmission gate TGA is turned on in a low resistance state close to a short circuit. For this reason, the voltage controlled oscillator VCOA transitions to a steady state at high speed. In the steady state, no current is supplied from the current source CSA to the nMOS transistor TB1, the transmission gate TGA is turned off in a high resistance state close to insulation, and the nMOS transistor is charged by the charge of the capacitor CB accumulated in the startup state. A bias voltage is supplied to the gate of TB2. Thus, in the steady state, the bias voltage is supplied to the nMOS transistor TB2 without supplying the current from the current source CSA to the nMOS transistor TB1, so that the power consumption in the steady state of the voltage controlled oscillator VCOA is reduced. The Therefore, the voltage controlled oscillator VCOA of the first embodiment can realize a short transition to the steady state and can reduce power consumption while keeping the phase noise low in the steady state. That is, it is possible to satisfy all three important characteristics of high-speed startability, low phase noise, and low power consumption.

  FIG. 3 shows a second embodiment of the present invention. In describing the second embodiment of the present invention, the same elements as those described in the first embodiment (FIG. 1) and the conventional example (FIG. 4) of the present invention are denoted by the same reference numerals and detailed. Description is omitted. The LC resonance type voltage controlled oscillator VCOB is configured by replacing the bias unit BUA with the bias unit BUB with respect to the voltage controlled oscillator VCOA of FIG.

  The bias unit BUB is configured by replacing the bias unit BUA of FIG. 1 by replacing the current source CSA, the transmission gate TGA, and the control circuit CTLA with the current source CSB, the transmission gate TGB, and the control circuit CTLB, respectively. The current source CSB performs a current supply operation for the nMOS transistor TB1 with one of two different supply capacities in accordance with an instruction from the control circuit CTLB. The transmission gate TGB is turned on at one of two different resistance values according to an instruction from the control circuit CTLB.

  The control circuit CTLB instructs the current source CSB to carry out a current supply operation to the nMOS transistor TB1 with a larger supply capability as the voltage controlled oscillator VCOB is turned on, and the transmission gate TGB has a lower resistance value. Instructs the transition to the ON state at. The control circuit CTLB instructs the current source CSB to perform a current supply operation with respect to the nMOS transistor TB1 with a smaller supply capability as the voltage controlled oscillator VCOB transitions to a steady state, and the transmission gate TGB has a higher one. Instructs the transition to the ON state with the resistance value of.

Here, the relationship between the potential fluctuation amount v1 of the gate of the nMOS transistor TB1 and the potential fluctuation amount V2 of the gate of the nMOS transistor TB2 is obtained by using the resistance value R of the transistor mission gate TGB and the capacitor value C of the capacitor CB. It is represented by the following formula (1).
v2 = {1 / (1 + jωCR)} × v1 (1)
Therefore, if the resistance value R of the transmission gate TGB and the capacitor value C of the capacitor CB are large, even if the drain current of the nMOS transistor TB1 is reduced, the potential fluctuation transmitted from the nMOS transistor TB1 to the gate of the nMOS transistor TB2, that is, noise Get smaller. Therefore, the resistance value R (higher resistance value) of the transistor mission gate TGB in the steady state of the voltage controlled oscillator VCOB is described above so that noise transmitted from the nMOS transistor TB1 to the gate of the nMOS transistor TB2 can be ignored. It is defined by the following equation (2) obtained by modifying equation (1).
R = (1 / jωC) × {(v1 / v2) −1} (2)
In the voltage controlled oscillator VCOB having the above-described configuration, in the start-up state, a large current is supplied from the current source CSB to the nMOS transistor TB1, and the transmission gate TGB is turned on in a low resistance state close to a short circuit. For this reason, the voltage controlled oscillator VCOB transitions to a steady state at high speed. In the steady state, the current source CSB supplies a small current to the nMOS transistor TB1 compared to the current supplied in the start-up state, and the transmission gate TGB has a high resistance defined by the above equation (2). Turn on in state. As described above, in a steady state, the current supplied from the current source CSB to the nMOS transistor TB1 is reduced, and noise is suppressed by the filter circuit including the transmission gate TGB and the capacitor CB, and the bias voltage is applied to the nMOS transistor TB2. Therefore, noise generated in the nMOS transistor TB1 is prevented from being transmitted to the gate of the nMOS transistor TB2, and the power consumption in the steady state of the voltage controlled oscillator VCOB is reduced. Therefore, the voltage controlled oscillator VCOB of the second embodiment can satisfy all three important characteristics, such as fast startability, low phase noise, and low power consumption, as in the first embodiment. Further, in the voltage controlled oscillator VCOB of the second embodiment, since a minute current is supplied from the nMOS transistor TB1 side to the nMOS transistor TB2 side in the steady state, it is effective, for example, when there is a leak in the capacitor CB.

  In the first and second embodiments described above, examples in which the main body portion and the bias portion are configured using nMOS transistors have been described, but the present invention is not limited to such embodiments. For example, at least one of the main body and the bias unit may be configured by replacing the power supply line and the ground line and replacing the nMOS transistor with a pMOS transistor.

  As mentioned above, although this invention was demonstrated in detail, the above-mentioned embodiment and its modification are only examples of this invention, and this invention is not limited to these. Obviously, modifications can be made without departing from the scope of the present invention.

It is explanatory drawing which shows 1st Embodiment of this invention. It is explanatory drawing which shows an example of the transmission gate of FIG. It is explanatory drawing which shows 2nd Embodiment of this invention. It is explanatory drawing which shows the prior art example of LC resonance type voltage controlled oscillator.

Explanation of symbols

BUA, BUB bias unit C1, C2, CB capacitor CSA, CSB current source CTLA, CTLB control circuit L1, L2 inductor MU body P1-P4 terminal SWN nMOS transistor SWP pMOS transistor T1, T2, TB1, TB2 nMOS transistor TGA, TGB Transmission gate VCOA, VCOB Voltage controlled oscillator VDD Power supply line VSS Ground line

Claims (2)

A main body that generates an oscillation signal having a desired frequency according to a control voltage, a current source, a first transistor connected in series to the current source, and a current mirror connection to the first transistor, and a bias applied to the main body A voltage controlled oscillator comprising a bias unit having a second transistor for supplying current,
The bias unit includes a switch circuit connected between the control terminals of the first and second transistors, and a capacitive element connected between the control terminal of the second transistor and a ground line ,
The current source performs a current supply operation to the first transistor when the voltage controlled oscillator is activated, and stops the current supply operation to the first transistor when the voltage controlled oscillator is in a steady state;
The switch circuit is turned on when the voltage controlled oscillator is activated, and is turned off when the voltage controlled oscillator is in a steady state. A main body that generates an oscillation signal having a desired frequency according to a control voltage, a current source, a first transistor connected in series to the current source, and a current mirror connection to the first transistor, and a bias applied to the main body A voltage controlled oscillator comprising a bias unit having a second transistor for supplying current,
The bias unit includes a switch circuit that is connected between the control terminals of the first and second transistors and functions as a resistance element, and a capacitive element that is connected between the control terminal of the second transistor and a ground line ,
The current source performs a current supply operation for the first transistor with a first supply capability when the voltage controlled oscillator is in a starting state, and performs a current supply operation for the first transistor with the first supply capability when the voltage controlled oscillator is in a steady state. With a smaller second supply capacity,
The voltage controlled oscillator, wherein the switch circuit is turned on with a first resistance value when the voltage controlled oscillator is in a starting state, and is turned on with a second resistance value higher than the first resistance value when the voltage controlled oscillator is in a steady state.

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