KR20050011316A - Differential voltage-to-current converter with improved linearity and voltage controlled oscillator including the same - Google Patents

Abstract

PURPOSE: A differential voltage-current converter and a voltage-controlled oscillator having the same are provided to reduce a gain of the voltage-controlled oscillator by using a differential voltage-current converter having improved linearity. CONSTITUTION: A differential voltage-current converter includes an input transistor pair(51), a control transistor pair(52), a first current mirror(53), a second current mirror(54), and a third current mirror(55). The input transistor pair receives a differential input signal pair. The control transistor pair is cross-coupled with each other and is coupled with the input transistor pair in parallel. The first current mirror duplicates the current flowing through one of the transistors in the input transistor pair. The second current mirror duplicates the duplicated current to an output terminal. The third current mirror duplicates the current flowing through the other of the transistors in the input transistor pair to the output terminal.

Description

Differential voltage-to-current converter with improved linearity and voltage controlled oscillator including the same}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to semiconductor integrated circuits, and more particularly, to differential voltage-to-current converters and voltage controlled oscillators (VCOs) using the same.

A voltage-to-current converter (VIC) is a circuit used in a voltage controlled oscillator (VCO), the most important block of a phase-locked loop (PLL), to convert voltage into current. It is a circuit. Phase locked loops (PLLs) are widely used in communication and control systems, including clock recovery, frequency synthesis, signal modulation and demodulation, and the like. One of the most important blocks in a PLL, the voltage controlled oscillator (VCO), has a great influence on the characteristics of the PLL.

The basic characteristic of a VCO is the slope of the frequency with respect to the input voltage. In other words, this slope is the sensitivity of how the frequency changes when the input voltage changes, which is called the gain of the VCO. In general, the noise characteristics of the PLL improve as the gain of the VCO decreases. The input voltage range of the VCO is limited to approximately 1.0 volts for a 1.8 volt supply voltage. If the required frequency range is narrow, the gain of the VCO can be reduced. However, if the required frequency range is wide, the gain of the VCO must be increased, which degrades the characteristics of the PLL.

FIG. 1 is a circuit diagram showing the configuration of a VCO. Referring to this, the VCO is a series of differential voltage current converters (VICs) 11 for converting and outputting voltages of differential input signal pairs INP and INN into current IOUT. A plurality of delay cells 12-15 connected and fed back to the first stage, each controlled by a current IOUT converted by the differential voltage current converter 11, and a final stage 15. And a buffer 16 for buffering and outputting a pair of output signals.

In the above-described VCO, a part of controlling the gain of the VCO is a differential voltage current converter (VIC) 11, and a general conventional VIC is shown in FIG.

Referring to FIG. 2, the conventional VIC includes an input transistor pair 21, a first current mirror 22, a second current mirror 23, a third current mirror 24, and a fourth current mirror. 25, a first current source I1, and a second current source I2.

The input transistor pair 21 receives the differential input signal pairs INP and INN. The first current mirror 22 mirrors the current flowing through one of the input transistor pairs 211, and the second current mirror 23 is reflected by the first current mirror 22. The current is reflected back to the output (Iout).

The third current mirror 24 reflects the current flowing through the other 212 of the input transistor pair and provides it to the output terminal Iout. The first current source I1 is connected to the power supply voltage VCC and supplies a current to the input transistor pair 21. The second current source I2 is also connected to the power supply voltage VCC and supplies a current, and the fourth current mirror 25 reflects the current supplied by the second current source I2 and provides it to the output terminal Iout.

In more detail, when INP is higher than INN, a large amount of current flows toward the input transistor 211 so that the current at the output terminal Iout increases. On the contrary, when INP is lower than INN, a large amount of current flows toward the input transistor 212 so that the current at the output terminal Iout decreases.

3 is a simulation result of the conventional VIC shown in FIG. Here, the X-axis represents the voltage difference INP-INN between the input signals and the Y-axis represents the current Iout of the output terminal. Referring to FIG. 3, although the voltage difference (INP-INN) between the input signals is -0.6 volts to 0.6 volts, the current Iout of the output stage is linearly expressed, but at higher voltages, the saturation state is reached. The abnormal current does not increase or decrease.

FIG. 4 simulates a change in frequency versus frequency of a VCO employing the conventional VIC shown in FIG. 2. Here the X-axis represents the voltage difference (INP-INN) between the input signals and the Y-axis represents the output frequency of the VCO. Referring to FIG. 4, as in the VIC simulation results shown in FIG. 3, the frequency change linearity of the VCO is limited and the gain is about 150 MHz / V.

However, if the linearity of the VIC is reduced, the linearity of the VCO is reduced, and eventually the gain of the VCO is increased, resulting in poor noise characteristics of the PLL.

Accordingly, an object of the present invention is to provide a differential voltage current converter (VIC) having improved linearity.

Another technical object of the present invention is to provide a voltage controlled oscillator (VCO) which reduces gain by providing a differential voltage current converter (VIC) having improved linearity.

BRIEF DESCRIPTION OF THE DRAWINGS In order to better understand the drawings cited in the detailed description of the invention, a brief description of each drawing is provided.

1 is a circuit diagram showing the configuration of a general voltage controlled oscillator (VCO).

2 is a circuit diagram showing a conventional differential voltage current converter (VIC).

3 is a simulation result of the conventional differential voltage current converter shown in FIG. 2.

FIG. 4 is a simulation result of a change in frequency vs. voltage of a VCO employing the conventional VIC shown in FIG. 2.

5 is a circuit diagram illustrating a differential voltage current converter (VIC) according to an embodiment of the present invention.

FIG. 6 shows a simulation result for the VIC according to the present invention shown in FIG. 5 and a simulation result for the conventional VIC shown in FIG. 2.

7 is a simulation result of the frequency change of the frequency of the VCO employing the VIC according to the present invention shown in Figure 5 and a simulation result of the voltage change frequency of the VCO employing the conventional VIC shown in Figure 2 It is shown together.

In accordance with an aspect of the present invention, a differential voltage current converter (VIC) includes an input transistor pair for receiving a differential input signal pair, and a control transistor connected to the input transistor pair in parallel and cross coupled to each other. A first current mirror for mirroring a current flowing through one of the pair of input transistors, and a second current for reflecting the current generated by the first current mirror again to provide to an output terminal. A mirror, and a third current mirror for reflecting a current flowing through the other of the pair of input transistors to provide to the output terminal.

The differential voltage current converter (VIC) according to the present invention includes a first current source connected to a power supply voltage and supplying current to the input transistor pair and the control transistor pair, a second current source connected to a power supply voltage and supplying current, And a fourth current mirror configured to reflect the current supplied by the second current source to provide to the output terminal.

The voltage controlled oscillator (VCO) according to the present invention for achieving the above another technical problem, the differential voltage current converter for converting the voltage of the differential input signal pair to output the current, and connected in series and the output of the final stage is first A plurality of delay cells, each of which is fed back and controlled by a current converted by the differential voltage current converter,

The differential voltage current converter includes an input transistor pair receiving a differential input signal pair, a control transistor pair connected in parallel to the input transistor pair and cross coupled to each other, and a current flowing through one of the input transistor pair. A first current mirror for mirroring, a second current mirror for reflecting back the current generated by the first current mirror and providing it to an output terminal, and flowing through the other of the pair of input transistors And a third current mirror that reflects current and provides the output to the output terminal.

The differential voltage current converter is provided by a first current source connected to a power supply voltage and supplying current to the input transistor pair and the control transistor pair, a second current source connected to a power supply voltage and supplying current, and supplied by the current source. And a fourth current mirror that reflects current and provides the output to the output terminal.

In order to fully understand the present invention, the operational advantages of the present invention, and the objects achieved by the practice of the present invention, reference should be made to the accompanying drawings illustrating preferred embodiments of the present invention and the contents described in the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like reference numerals in the drawings denote like elements.

5 is a circuit diagram illustrating a differential voltage current converter (VIC) according to an embodiment of the present invention.

5, an input transistor pair 51, a control transistor pair 52, a first current mirror 53, a second current mirror 54, a third current mirror 55, and a fourth current mirror 56. ), A first current source I1, and a second current source I2. That is, the differential voltage current converter VIC according to the embodiment of the present invention further includes a control transistor pair 52 as compared to the conventional VIC shown in FIG. 2.

The input transistor pair 51 receives the differential input signal pairs INP and INN and consists of two PMOS transistors 511 and 512. The control transistor pair 52 is composed of two PMOS transistors 521 and 522 connected in parallel to the input transistor pair 51 and cross coupled to each other.

The first current mirror 53 mirrors the current flowing through one of the input transistor pairs 511, and the second current mirror 54 is reflected by the first current mirror 53. The current is reflected back to the output (Iout). The first current mirror 53 is composed of two NMOS transistors 531, 532 and the second current mirror 54 is composed of two PMOS transistors 541, 542.

The third current mirror 55 reflects the current flowing through the other one 512 of the input transistor pair and provides it to the output terminal Iout. The third current mirror 55 is composed of two NMOS transistors 551 and 552.

The first current source I1 is connected to the power supply voltage VCC and supplies current to the input transistor pair 51 and the control transistor pair 52. The second current source I2 is also connected to the power supply voltage VCC and supplies a current, and the fourth current mirror 56 reflects the current supplied by the second current source I2 and provides it to the output terminal Iout.

More specifically, the VIC according to the present invention differs from the prior art of FIG. 2 in that the control transistor pair 52 cross-coupled in parallel with the input transistor pair 51 receiving the input signal pairs INP and INN is provided. This is an added point.

In the prior art, as in the simulation of FIG. 3, the current Iout of the output stage no longer increases or decreases below -0.6 volts and 0.6 volts or more. In other words, a certain amount of differential input voltage must be applied for the VIC to respond to the input signal.

Therefore, the present invention aims to reduce this area by adding a cross-coupled control transistor pair 52 to the input terminal. For example, when no current flows through the input transistor 511, the current flows through the control transistor 521 so that the sum of the two currents is linear in a wide range with respect to the voltage change of the input signal INP.

FIG. 6 shows a simulation result for the VIC according to the present invention shown in FIG. 5 and a simulation result for the conventional VIC shown in FIG. 2. Here, the X-axis represents the voltage difference INP-INN between the input signals and the Y-axis represents the current Iout of the output terminal.

Referring to FIG. 6, in the prior art B, although the voltage difference INP-INN between the input signals is about -0.6 volts to about 0.6 volts, a change in the current Iout of the output terminal is linear, but more than that voltage. At saturation, the current no longer increases or decreases. On the other hand, in the present invention (A), it can be seen that the current (Iout) of the output stage changes linearly while the voltage difference (INP-INN) between the input signals varies from about -1.2 volts to 1.2 volts. This result means that the linearity of the VIC according to the present invention is improved by about 2 times compared to the prior art.

7 is a simulation result of the frequency change of the frequency of the VCO employing the VIC according to the present invention shown in FIG. 5 and a simulation result of the frequency change of the frequency of the VCO employing the conventional VIC shown in FIG. It is shown together. Here the X-axis represents the voltage difference (INP-INN) between the input signals and the Y-axis represents the output frequency of the VCO.

Referring to FIG. 7, it can be seen that the gain of the VCO in the present invention (C) is approximately 80 MHz / V, which is reduced by half compared to the gain of the VCO in the prior art (D) of 150 MHz / V.

Therefore, the VCO employing the VIC according to the present invention shown in FIG. 5 has the advantage of reducing the gain in half if the same controllable frequency range of the VCO is maintained as compared with the conventional VIC. Maintaining the gain has the advantage of doubling the controllable frequency range.

The best embodiment has been disclosed in the drawings and specification above. Although specific terms have been used herein, they are used only for the purpose of describing the present invention and are not intended to limit the scope of the invention as defined in the claims or the claims. Therefore, those skilled in the art will understand that various modifications and equivalent other embodiments are possible from this. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

As described above, in the VIC according to the present invention, linearity is improved. Therefore, the voltage controlled oscillator (VCO) employing the differential voltage current converter (VIC) according to the present invention can reduce the gain in half if the controllable frequency range of the VCO remains the same as that of the conventional VCO. It also has the advantage of doubling the controllable frequency range if the same gain is maintained.

Claims (6)

An input transistor pair for receiving a differential input signal pair; A control transistor pair coupled in parallel to the input transistor pair and cross coupled to each other; A first current mirror for mirroring current flowing through one of the input transistor pairs; A second current mirror which reflects the current generated by the first current mirror and reflects it back to an output terminal; And And a third current mirror for reflecting a current flowing through the other of the pair of input transistors and providing it to the output terminal. The method of claim 1, And a current source coupled to a supply voltage and supplying current to the pair of input transistors and to the pair of control transistors. The method of claim 1, A current source connected to the power supply voltage and supplying current; And And a fourth current mirror which reflects the current supplied by the current source and provides it to the output terminal. A differential voltage current converter for converting and outputting a voltage of a differential input signal pair into a current; And Having a plurality of delay cells connected in series and having an output of the last stage fed back to the first stage, each controlled by a current converted by the differential voltage current converter, The differential voltage current converter, An input transistor pair for receiving a differential input signal pair; A control transistor pair coupled in parallel to the input transistor pair and cross coupled to each other; A first current mirror for mirroring current flowing through one of the input transistor pairs; A second current mirror which reflects the current generated by the first current mirror and reflects it back to an output terminal; And And a third current mirror configured to reflect current flowing through the other of the pair of input transistors to provide to the output terminal. The method of claim 4, wherein the differential voltage current converter, And a current source coupled to a power supply voltage for supplying current to the input transistor pair and the control transistor pair. The method of claim 4, wherein the differential voltage current converter, A current source connected to the power supply voltage and supplying current; And And a fourth current mirror which reflects the current supplied by the current source and provides it to the output terminal.