CN109828629B

CN109828629B - VCO circuit

Info

Publication number: CN109828629B
Application number: CN201711189414.3A
Authority: CN
Inventors: 高鹏; 乔峻石; 赖玠玮
Original assignee: Beijing Ziguang Zhanrui Communication Technology Co Ltd
Current assignee: Beijing Ziguang Zhanrui Communication Technology Co Ltd
Priority date: 2017-11-23
Filing date: 2017-11-23
Publication date: 2020-10-09
Anticipated expiration: 2037-11-23
Also published as: CN109828629A

Abstract

The embodiment of the application discloses a VCO circuit, which is used for improving the range of VCO control voltage and improving the capability of the VCO in restraining power supply voltage noise and interference. The VCO circuit in the embodiment of the present application includes: the filter module comprises a filter module, a voltage-current conversion module and a CCO module, wherein one end of a first filter and one end of a second filter in the filter module are connected to a first node, the first node is connected with a control voltage, the other end of the first filter is connected to a power supply, and the other end of the second filter is connected with the ground; the grid electrode of a first MOS tube and the grid electrode of a second MOS tube in the voltage-current conversion module are connected to a second node, the second node is connected with the first node, the drain electrode of the first MOS tube and the drain electrode of the second MOS tube are connected to a third node, the third node is connected with the CCO module, the source electrode of the first MOS tube is connected with one end of a first resistor, the other end of the first resistor is connected with the ground, the source electrode of the second MOS tube is connected with one end of a second resistor, and the other end of the second resistor is connected with a power supply.

Description

VCO circuit

Technical Field

The present application relates to the field of electronics, and more particularly, to a VCO circuit.

Background

A Voltage Controlled Oscillator (VCO) is an indispensable module in a phase locked loop. In a baseband phase locked loop, a common structure is a current-controlled circular Complementary Metal Oxide Semiconductor (CMOS) VCO. Under the application of low voltage and low power consumption, the input control voltage range of the VCO with the structure is smaller, the frequency adjusting range required by the VCO cannot be reduced, the gain of the VCO is improved, and the overall noise performance of the phase-locked loop is poor. In addition, the actual power supply of the VCO usually comes from an on-chip low dropout regulator (LDO) to isolate the interference from the power supply. However, in low-voltage and low-power applications, both the power supply rejection capability and the self-output noise performance of the LDO are not very good. If the VCO itself does not have a good power supply noise suppression capability, the finally designed noise performance will be poor, or the power consumption is relatively large, and the advantages of low voltage and low power consumption are lost.

The combination of a current-controlled ring oscillator and a voltage-to-current converter is a popular implementation of a VCO in a baseband phase-locked loop. In a VCO of this structure, the control of the frequency by voltage is split into the control of the current by voltage and the control of the frequency by current. The conversion from voltage to current is mainly realized by transconductance of a transistor, and the transistor is required to work in a saturation region to provide stable and reliable voltage and current control. In low voltage applications, if only the conventional single-tube source follower structure is used to control the oscillator operating current, then a significant voltage margin is wasted in ensuring transistor saturation. The control voltage needs to be greater than the supply voltage of the ring oscillator plus the threshold voltage of one transistor. In low-voltage application under certain processes, even if a native transistor is adopted, the voltage value is still considerable, and the variation range of the control voltage is severely limited. The limitation of the control voltage range further results in an increase in the VCO gain, which is detrimental to the overall noise for most phase locked loops.

To extend the control voltage range of a VCO, the prior art is shown in fig. 1 a. The scheme of fig. 1a adopts a voltage-current converter with a differential structure, and a feedback amplifier is added, so that the control of the control voltage on the power supply voltage of the oscillator is ensured through the high gain of the amplifier. Because the current tube of the oscillator is not directly controlled, a larger control voltage variation range can be realized as long as the input voltage range of the amplifier is larger.

In a System On Chip (SOC) Chip, various noises are often mixed into a power supply voltage, and the sources thereof include DC-DC interference, digital block noise, LDO noise, and the like. The VCO is affected by a change in the supply voltage similarly to an additional control voltage, the specific value of which can be expressed as a value similar to the VCO gain, called K_VDD. Variation of VCO supply voltage by K_VDDThe VCO frequency is modulated, phase deviation is introduced, the noise performance of the VCO and a phase-locked loop is deteriorated, and most of the VCOs have larger K_VDD。

In order to improve the power supply noise suppression capability of the VCO, as shown in fig. 1b and fig. 1c, an additional reverse K may be added to the original VCO circuit_VDDSmall circuit of (2), with the original forward direction K_VDDCompensation is performed, so that better power supply rejection capability is obtained. The embodiment corresponding to fig. 1b introduces an NMOS transistor at the delay cell output of the VCO, which compensates for the variation of its impedance with supply voltageThe influence of the supply voltage. The corresponding embodiment of fig. 1c uses a similar method, except that the impedance of the NMOS transistor is replaced by the impedance of the resistor-capacitor network formed by the MOS transistors. Because the delay of the uncompensated delay unit is in negative correlation with the power supply voltage (or the oscillation frequency of the VCO is in positive correlation with the power supply voltage), the additionally introduced compensation circuit enables the delay of the delay unit to generate a positive correlation effect with the power supply voltage (or the oscillation frequency of the VCO is in negative correlation with the power supply voltage), and the effect of the compensation circuit is properly adjusted, so that the compensation can be performed with the original characteristic, and the power supply correlation close to 0 can be obtained.

In the above two prior arts, the circuit structure is complicated. In terms of extending the VCO control voltage range, as in the embodiment corresponding to fig. 1a, a four-input and two-output amplifier is used, which needs to meet the loop bandwidth requirement of the phase-locked loop, and needs a suitable common mode negative feedback circuit to stabilize the common mode. This amplifier itself is also a significant noise source for the VCO. Moreover, due to the loop bandwidth requirements, a filter cannot be used to filter out these noises. In the aspect of improving the power supply noise suppression capability, the main disadvantage in the embodiments corresponding to fig. 1b and fig. 1c is also the addition of an additional circuit, that is, the design complexity is increased, and a noise source is introduced.

Disclosure of Invention

The embodiment of the application provides a VCO circuit, which is used for improving the range of VCO input control voltage and improving the suppression capability of the VCO on power supply voltage noise and interference under the condition that no additional circuit is added.

The VCO circuit provided in the embodiment of the present application includes: the filter module comprises a first filter and a second filter, wherein one end of the first filter and one end of the second filter are connected to a first node, the first node is connected with a control voltage, the other end of the first filter is connected to a power supply, and the other end of the second filter is connected to the ground; the voltage and current conversion module comprises a first MOS tube, a second MOS tube, a first resistor and a second resistor, wherein the grid electrode of the first MOS tube and the grid electrode of the second MOS tube are connected to a second node, the second node is connected with the first node, the drain electrode of the first MOS tube and the drain electrode of the second MOS tube are connected to a third node, the third node is connected with the CCO module, the source electrode of the first MOS tube is connected with one end of the first resistor, the other end of the first resistor is connected with the ground, the source electrode of the second MOS tube is connected with one end of the second resistor, and the other end of the second resistor is connected into a power supply.

According to the technical scheme, the embodiment of the application has the following advantages: in the embodiment of the application, the NMOS tube and the PMOS tube are simultaneously used in the voltage-current conversion module, and as long as the sum of the absolute values of the threshold voltages of the two MOS tubes is less than or equal to the power supply voltage or slightly greater than the power supply voltage, the control voltage variation range of the voltage-current conversion module can at least reach the power supply voltage to the ground, and the range of the VCO input control voltage can be improved; the filter module in this application has been divided into two parts of connecting power respectively, ground, can adjust the response of control voltage to the power noise through proper proportion distribution, and then adjusts the response of NMOS pipe and PMOS pipe to the power noise in the voltage current conversion module, makes both compensate each other, has reduced the CCO electric current and has received the influence of power noise, can improve the suppression ability of VCO to power voltage noise and interference.

Drawings

FIG. 1a is a schematic diagram of one embodiment of a prior art VCO circuit;

FIG. 1b is a schematic diagram of one embodiment of a delay cell in a prior art VCO circuit;

FIG. 1c is a schematic diagram of another embodiment of a delay cell in a prior art VCO circuit;

FIG. 2 is a schematic diagram of an embodiment of a VCO circuit in an embodiment of the present application;

FIG. 3 is a schematic diagram of an embodiment of a voltage-to-current conversion module according to an embodiment of the present disclosure;

FIG. 4 is a schematic diagram of another embodiment of a voltage-to-current conversion module in an embodiment of the present application;

FIG. 5 is a schematic diagram of another embodiment of a voltage-to-current conversion module in an embodiment of the present application;

fig. 6 is a schematic diagram of an embodiment of a voltage-current conversion module and a filter module in the embodiment of the present application.

Detailed Description

The embodiment of the application provides a VCO circuit, which is used for improving the range of VCO control voltage and improving the capability of the VCO in inhibiting power supply voltage noise and interference under the condition that no additional circuit is added.

The terms "first," "second," "third," "fourth," and the like in the description and in the claims of the present application and in the drawings described above, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It will be appreciated that the data so used may be interchanged under appropriate circumstances such that the embodiments described herein may be practiced otherwise than as specifically illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

Referring to fig. 2, the VCO circuit according to the embodiment of the present application mainly includes the following components: a filter module 100, a voltage to current conversion module 200 and a current controlled oscillator CCO module 300.

The filter module 100 includes a first filter 101 and a second filter 102, wherein one end of the first filter 101 and one end of the second filter 102 are connected to a first node 103, the first node 103 is connected to a control voltage, the other end of the first filter 101 is connected to a power supply, and the other end of the second filter 102 is connected to ground;

the voltage-current conversion module 200 includes a first Metal Oxide Semiconductor Field Effect Transistor (MOSFET) (hereinafter referred to as MOS Transistor) 201, a second MOS Transistor 202, a first resistor 203, and a second resistor 204, a gate of the first MOS Transistor 201 and a gate of the second MOS Transistor 202 are connected to a second node 205, the second node 205 is connected to the first node 103, a drain of the first MOS Transistor 201 and a drain of the second MOS Transistor 202 are connected to a third node 206, the third node 206 is connected to the CCO module, a source of the first MOS Transistor is connected to one end of the first resistor 203, another end of the first resistor 203 is connected to ground, a source of the second MOS Transistor 202 is connected to one end of the second resistor 204, and another end of the second resistor 204 is connected to a power supply.

The CCO module 300 includes a third MOS transistor 301, a fourth MOS transistor 302, and a bias current I _BIAS303 and a Ring current control oscillator Ring CCO304, the source electrode of the third MOS tube 301 is connected with a power supply, and the drain electrode of the third MOS tube 301 passes through I _BIAS303 is grounded, the gate of the third MOS tube 301 is connected to the gate of the fourth MOS tube 302, the source of the fourth MOS tube 302 is connected to the power supply, the drain of the fourth MOS tube 302 and one end of the Ring CCO304 are connected to the fourth node 306, the fourth node 306 is connected to the third node 206, and the other end of the Ring CCO304 is connected to ground.

The current mirror formed by connecting the gate of the third MOS transistor 301 with the gate of the fourth MOS transistor 302 can provide a fixed current bias for the RingCCO304, and the fixed current does not need to be controlled by the control voltage V_CTRLThe control of (2) does not need to consider the response speed, and because the current mirror has noise, the embodiment of the present application may add the RC low pass filter 305 to filter the noise of the current mirror.

It should be noted that the actual power supply of the VCO circuit in this application may come from an LDO on chip to isolate the interference from the power supply.

It should be noted that in the embodiment of the present application, the first MOS transistor 101 is an NMOS transistor, the second MOS transistor 102 is a PMOS transistor, the third MOS transistor 301 is a PMOS transistor, and the fourth MOS transistor 302 is a PMOS transistor.

It should be noted that, in the embodiment of the present application, both the first filter 101 and the second filter 102 are Low Pass Filters (LPF), and have the same structure but different impedances.

The voltage-current conversion module 200 is essentially a push-pull amplifier with an input from the VCO circuitControl voltage V of_CTRLControl, the output is connected to Ring CCO304 of CCO module 300. As shown in fig. 3, at a control voltage V_CTRLWhen the voltage is higher, the second MOS transistor 202 is turned off, the first MOS transistor 201 is turned on, and the voltage-current conversion module 200 extracts a certain amount of current from the fourth MOS transistor 302; as shown in fig. 4, when the voltage V is controlled_CTRLWhen the current is lower, the first MOS transistor 201 is cut off, the second MOS transistor 202 is opened, and the module outputs current to the CCO; as shown in fig. 5, at a control voltage V_CTRLWhen the current is moderate, the first MOS transistor 201 and the second MOS transistor 202 are simultaneously opened, and the output or extraction current is determined by the difference of the absolute values of the currents of the first MOS transistor 201 and the second MOS transistor 202. At a control voltage V_CTRLIn the process of reduction, the output current value changes from negative to positive monotonically, and the conversion from voltage to current is realized.

When controlling the voltage V_CTRLIs relatively high, i.e. when V_CTRL>V_DD-|V_TH2When | is, the transconductance of the voltage-current conversion module 200 is:

wherein, V_CTRLFor controlling the voltage, V_TH2Is the threshold voltage, V, of the second MOS transistor 202_DDIs a supply voltage, G_M-HIs the transconductance, g, of the voltage-to-current conversion module 200_m1Is the transconductance of the first MOS transistor 201, R₁Is the resistance of the first resistor 203.

When controlling the voltage V_CTRLRelatively low, i.e. when V_CTRL<|V_TH1When | is, the transconductance of the voltage-current conversion module 200 is:

wherein, V_CTRLFor controlling the voltage, V_TH1Is the threshold voltage, G, of the first MOS transistor 201_M-LIs the transconductance, g, of the voltage-to-current conversion module 200_m2Is the transconductance of the second MOS transistor 202, R₂Of a second resistor 204The resistance value.

When controlling the voltage V_CTRLModerate, i.e. when | V_TH1|<V_CTRL<V_DD-|V_TH2When | is, the transconductance of the voltage-current conversion module 200 is:

wherein, V_CTRLFor controlling the voltage, V_TH1Is the threshold voltage, V, of the first MOS transistor 201_TH2Is the threshold voltage, V, of the second MOS transistor 202_DDIs a supply voltage, G_M-MIs the transconductance, g, of the voltage-to-current conversion module 200_m1Is the transconductance of the first MOS transistor 201, g_m2Is the transconductance of the second MOS transistor 202, R₁Is the resistance value, R, of the first resistor 203₂Is the resistance of the second resistor 204.

In the above formula, V_TH1May be 350 millivolts, V_TH2May be 350 millivolts, V_DDMay have a value of 900 millivolts, in practical applications, V_TH1、V_TH2And V_DDThe numerical value of (b) may be other numerical values, and is not limited herein.

Since the voltage-current conversion module circuit in the application uses the NMOS transistor (the first MOS transistor 201) and the PMOS transistor (the second MOS transistor 202) at the same time, as long as the sum of the absolute values of the threshold voltages of the two transistors is less than or equal to the power supply voltage or slightly greater than the power supply voltage, the control voltage variation range that the voltage-current conversion module 200 can accept can at least reach the power supply voltage to the ground, and the limitation of the VCO control voltage range is eliminated. In practical application, the native NMOS transistor is used as the first MOS transistor 201, and the threshold voltage is low, which is helpful to ensure the total control voltage range.

The source degeneration resistors (i.e. the first resistor 203 and the second resistor 204) are added to the sources of the first MOS transistor 201 and the second MOS transistor 202, and the function of the source degeneration resistors is to limit the maximum transconductance of the transistors, and when the control voltage is too high, the transconductance of the first MOS transistor 201 is limited to 1/R₁Otherwise, the transconductance of the PMOS tube is limited to 1/R₂Is provided withWhich helps to improve the linearity of the voltage-to-current conversion module 200.

The VCO circuit in the embodiment of the present application may improve the range of the VCO control voltage through the voltage-current conversion module 200 formed by the first MOS transistor 201, the second MOS transistor 202, the first resistor 203, and the second resistor 204 without adding an additional circuit.

Referring to fig. 6, in the embodiment of the present application, the filter is divided into two parts (a first filter 101 and a second filter 102), the first filter 101 is connected to a power supply, the second filter 102 is connected to ground, and the impedances of the two parts are identical to the original impedance after being connected in parallel, so that the impedance can be consistent with that of the single low pass filter LPF in the phase-locked loop. This is split in half in this application to compensate for the effects of power supply noise by appropriate impedance scaling in cooperation with the voltage to current conversion module of this application. The main mechanisms by which supply noise affects VCO performance are as follows: the change of the power supply voltage is reflected to V in a certain proportion_CTRLThen, the transconductance of the first MOS transistor 201 and the second MOS transistor 202 generates current change, and the current change is output to the following CCO module 300, so that the operating frequency of the CCO module is affected, and a phase deviation is caused. Adjustment of the ratio of the two filters changes the ratio at which the supply voltage change is reflected on VCTRL, thereby adjusting the effect of the supply voltage change on the CCO frequency.

Let the voltage of the power supply noise be V_NWhen the impedance ratio of the first filter 101 to the second filter 102 is k, V is_CTRLThe voltage due to power supply noise is:

the drain output current of M1 due to power supply noise is:

the drain output current of M2 due to power supply noise is:

it is clear that_N1Is a negative value and I_N2The impedance ratio k is adjusted to be a positive value, so that the power response outputs of the voltage-current conversion module 200 are mutually cancelled, and finally, the residual power noise response current can be small. In practical applications, the fixed bias current portion (the fourth MOS transistor 302) in the CCO also contributes to a certain power supply noise response current due to the channel length modulation effect, and this portion can be compensated by adjusting the value of k.

In the VCO circuit in the embodiment of the present application, the voltage-current conversion module 200 formed by the first MOS transistor 201, the second MOS transistor 202, the first resistor 203, and the second resistor 204, and the filter module 100 formed by the first filter 101 and the second filter 102 can implement the function of power supply noise compensation by only the connection allocation of the filters without adding an additional circuit, thereby improving the capability of the VCO in suppressing power supply voltage noise and interference.

The above embodiments are only used for illustrating the technical solutions of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions in the embodiments of the present application.

Claims

1. A Voltage Controlled Oscillator (VCO) circuit comprising a filter module, a voltage to current conversion module, and a Current Controlled Oscillator (CCO) module, comprising:

the filter module comprises a first filter and a second filter, one end of the first filter and one end of the second filter are connected to a first node, the first node is connected with a control voltage, the other end of the first filter is connected to a power supply, and the other end of the second filter is connected to the ground;

the voltage and current conversion module comprises a first MOS tube, a second MOS tube, a first resistor and a second resistor, wherein the grid electrode of the first MOS tube and the grid electrode of the second MOS tube are connected to a second node, the second node is connected with the first node, the drain electrode of the first MOS tube and the drain electrode of the second MOS tube are connected to a third node, the third node is connected with the CCO module, the source electrode of the first MOS tube is connected with one end of the first resistor, the other end of the first resistor is connected with the ground, the source electrode of the second MOS tube is connected with one end of the second resistor, and the other end of the second resistor is connected with a power supply;

the first MOS tube is an NMOS tube;

the second MOS tube is a PMOS tube.

2. The VCO circuit of claim 1, wherein the CCO module comprises a third MOS transistor, a fourth MOS transistor, a bias current I_BIASAnd a Ring current control oscillator Ring CCO, wherein the source electrode of the third MOS tube is connected with a power supply, and the drain electrode of the third MOS tube passes through the I_BIASThe grid electrode of the third MOS tube is connected with the grid electrode of the fourth MOS tube through an RC filter, the source electrode of the fourth MOS tube is connected with a power supply, the drain electrode of the fourth MOS tube is connected with the current input end of the Ring CCO to a fourth node, the fourth node is connected with the third node, and the other end of the Ring CCO is connected with the ground.

3. The VCO circuit of claim 2, wherein the CCO module further comprises an RC filter for filtering noise of a current mirror, the current mirror being formed by the third MOS transistor and the fourth MOS transistor.

4. The VCO circuit according to any of claims 1 to 3, wherein said third MOS transistor is a PMOS transistor.

5. The VCO circuit according to any of claims 1 to 3, wherein said fourth MOS transistor is a PMOS transistor.

6. The VCO circuit according to any of claims 1 to 3, wherein when the control voltage is below a first threshold value, the first MOS is turned off and the second MOS is turned on.

7. The VCO circuit according to any of claims 1 to 3, wherein said first MOS is turned on and said second MOS is turned on when said control voltage is within a range of a first threshold and a second threshold.

8. The VCO circuit according to any of claims 1 to 3, wherein said first MOS is turned on and said second MOS is turned off when said control voltage is higher than a second threshold.