Current-mode logic circuit

This Application claims priority of China Patent Application No. 201610841642.3, filed on Sep. 22, 2016, the entirety of which is incorporated by reference herein.

The invention relates to high-speed transmission, and more particularly, to a current-mode logic circuit.

With the development of semiconductor technology, the operating frequencies of circuits are continuously increasing, especially in cases related to high-speed transmission, wherein when speeds can reach 10 GHz or above, the operating speeds of CMOS logic-based unit circuits will be limited. In high-speed transmission, current-mode logic (CML) circuits are usually used to replace regular CMOS logic circuits.

According to current technology, since different high-speed signals, such as high-speed data signals of a display port (DP), a high definition multimedia interface (HDMI), a mobile high-definition link (MHL), and a universal serial bus (USB), have different requirements for certain parameters, such as a common-mode voltage of differential output signals, a current consumed by a transmitter terminal, and so on. During transmission processes, the current CIVIL circuits with fixed parameters are only suitable for one specific application, one CML circuit cannot be flexibly applied to various applications.

Thus, how to make common-mode current and consumed current adjustable is an important issue to be solved in order to achieve the purpose of flexibly applying one CML in various applications.

Thus, the present invention provides a current-mode logic circuit.

An exemplary embodiment of a current-mode logic circuit is provided. The current-mode logic circuit comprises a transmitter module. The transmitter module comprises an output impedance circuit, a switch circuit, and a current source. The output impedance circuit provides an adjustable output resistor. The adjustable output resistor comprises floating resistors and/or pull-up resistors. The switch circuit is coupled to the output impedance circuit. The switch circuit receives differential input signals, outputs differential output signals, and controls high-low level switching of the differential input signals and the differential output signals according to the adjustable output resistor. The current source is coupled to the output impedance circuit and the switch circuit. The current source provides currents to the output impedance circuit and the switch circuit. The floating resistors are resistors coupled between the differential output signals, and the pull-up resistors are resistors coupled between the differential output signals and a power source.

According to the embodiment provided by the present invention, the current-mode logic circuit controls high-low level switching of the differential input signals and the differential output signals according to the adjustable output resistor output from the output impedance circuit, thereby making the common voltage of the differential output signals and the current consumed by the transmitter module adjustable. Thus, the current-mode logic circuit can be flexibly applied in various high-speed signal transmission applications.

A detailed description is given in the following embodiments with reference to the accompanying drawings.

The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:

FIG. 1 is a schematic diagram showing a structure of a current-mode logic circuit according to a first embodiment;

FIG. 2 is a schematic diagram showing a circuit principle of a current-mode logic circuit according to a second embodiment;

FIG. 3 is a schematic diagram showing an equivalent circuit when the transmitter module shown in FIG. 2 operates in a first operation mode;

FIG. 4 is a schematic diagram showing an equivalent circuit when the transmitter module shown in FIG. 2 operates in a second operation mode; and

FIG. 5 is a schematic diagram showing an equivalent circuit when the transmitter module shown in FIG. 2 operates in a third operation mode.

Certain terms are used throughout the specification and following claims to refer to particular components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. The specification and following claims do not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms “include” and “comprise” are used in an open-ended fashion, and thus should be interpreted to mean “include, but not limited to . . . ”. Also, the term “couple” is intended to mean either an indirect or direct electrical connection. Accordingly, if a first device is coupled to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices or connections.

To better understand the technical aspects of the present invention, the following embodiments of the invention will be described in detail by referring to the drawings.

FIG. 1 is a schematic diagram showing a structure of a current-mode logic circuit according to a first embodiment. As shown in FIG. 1 , a current-mode logic circuit 100 comprises a transmitter module 1 and a receiver module 2 .

In the embodiment, the transmitter module 1 and the receiver module 2 are disposed in different devices. The transmitter module 1 transmits differential signals to the receiver module 2 through a connection line 3 .

Specifically, the transmitter module 1 comprises an output impedance circuit 11 , a switch circuit 12 , and a current source 13 .

The output impedance circuit 11 is coupled to provide an adjustable output resistor including floating resistors and/or pull-up resistors.

The switch circuit 12 is coupled to the output impedance circuit 11 and the receiver module 2 . The switching circuit 12 receives differential input signals, outputs differential output signals to the receiver module 2 , and controls high-low level switching of the differential input signals and the differential output signals according to the adjustable output resistor output from the output impedance circuit 11 .

The current source 13 is coupled to the output impedance circuit 11 and the switch circuit 12 . The current source 13 provides currents to the output impedance circuit 11 and the switch circuit 12 .

The floating resistors are resistors coupled between the differential output signals. The pull-up resistors are resistors coupled between the differential output signals and a power source.

In the embodiment above, the current-mode logic circuit controls high-low level switching of the differential input signals and the differential output signals according to the adjustable output resistor output from the output impedance circuit, thereby making the common voltage of the differential output signals and the current consumed by the transmitter module adjustable. Thus, the current-mode logic circuit can be flexibly applied to various high-speed signal transmission applications.

FIG. 2 is a schematic diagram showing a circuit principle of a current-mode logic circuit according to a second embodiment. As shown in FIG. 2 , a current-mode logic circuit 200 comprises a transmitter module 20 and a receiver module 30 .

In the embodiment, the transmitter module 20 and the receiver module 30 are disposed in different devices. The transmitter module 20 transmits differential signals OUTP and OUTN to the receiver module 30 through a connection line 40 .

The transmitter module 20 comprises an output impedance circuit 21 , a switching circuit 22 , and a current source 23 . The output impedance circuit 21 is coupled to provide an adjustable output resistor including floating resistors and/or pull-up resistors. The switch circuit 22 receives differential input signals DP and DN, outputs the differential output signals OUTP and OUTN, and controls high-low level switching of the differential input signals DP and DN and the differential output signals OUTP and OUTN according to the adjustable output resistor. The current source 23 provides currents to the output impedance circuit 21 and the switch circuit 22 .

Specifically, the output impedance circuit 21 comprises a plurality of output impedance sub-circuits 221 which are coupled in parallel. Each output impedance sub-circuit 211 comprises a first resistor R 1 , a second resistor R 2 , a first switch K 1 , a second switch K 2 , and a third switch K 3 . Terminals of all the first resistors R 1 on one side are coupled together at a first common terminal Q 1 . Terminals of all the second resistors R 2 on one side are coupled together at a second common terminal Q 2 . For each output impedance sub-circuit 211 , the other terminal of the first resistor R 1 is coupled to one terminal of the first switch K 1 and one terminal of the second switch K 2 , the other terminal of the first switch K 1 is coupled to the other terminal of the second resistor R 2 and one terminal of the third switch K 3 , and the other terminal of the second switch K 2 is coupled to the other terminal of the third switch K 3 and then coupled to a first power source VDD 1 .

The switch circuit 22 comprises a first transistor N 1 and a second transistor N 2 . Gates of the first transistor N 1 and the second transistor N 2 receive differential input signals DP and DN respectively. Drains of the first transistor N 1 and the second transistor N 2 are coupled to the first common node Q 1 and the second common node Q 2 respectively. Sources of the first transistor N 1 and the second transistor N 2 are coupled together and then coupled to the positive terminal of the current source 23 . The negative terminal of the current source 23 is coupled to the ground.

Preferably, the transmitter module 20 further comprises a protection circuit 24 coupled between the output impedance circuit 21 and the switch circuit 22 . The protection circuit 24 comprises a third transistor N 3 and a fourth transistor N 4 . Gates of the third transistor N 3 and the fourth transistor N 4 receive a control signal Vcas. Sources of the third transistor N 3 and the fourth transistor N 4 are coupled to the drains of the first transistor N 1 and the second transistor N 2 respectively. Drains of the third transistor N 3 and the fourth transistor N 4 are coupled to the first common node Q 1 and the second common node Q 2 respectively.

The first common node Q 1 and the second common node Q 2 are coupled to one terminal of the connection line 40 for outputting the differential output signals OUTP and OUTN.

Specifically, the receiver module 30 comprises an input impedance circuit 301 . The input impedance circuit 301 provides an input resistor. The input impedance circuit 301 comprises a first input resistor RS 1 and a second input resistor RS 2 . One terminal of the first input resistor RS 1 and one terminal of the second input resistor RS 2 are coupled together and then coupled to the second power source VDD 2 . The other terminal of the first input resistor RS 1 and the other terminal of the second input resistor RS 2 are coupled to the other terminal of the connection line 40 to receive the differential output signals OUTP and OUTN respectively.

In the embodiment, according to the different operation states of the first switch K 1 , the second switch K 2 , and the third switch K 3 in each output impedance sub-circuits 221 , the transmitter module 20 can operate in three different operation modes.

When the first switch K 1 of each output impedance sub-circuit 221 is turned on and the second switch K 2 and the third switch K 3 thereof are turned off, the output resistor provided by the output impedance circuit 21 may be floating resistors, and the transmitter module 20 operates in a first operation mode.

Referring to FIG. 3 , FIG. 3 is a schematic diagram showing an equivalent circuit when the transmitter module shown in FIG. 2 operates in the first operation mode. As shown in FIG. 3 , the first floating resistor R 1 ′ and the second floating resistor R 2 ′ are the corresponding equivalent resistors of the output impedance circuit 21 .

One terminal of the first floating resistor R 1 ′ is coupled to one terminal of the second floating resistor R 2 ′. The other terminal of the first floating resistor R 1 ′ and the other terminal of the second floating resistor R 2 ′ are coupled to the first common node Q 1 and the second common node Q 2 respectively.

When the transmitter module 20 operates in the first operation mode, if the resistance of the first input resistor RS 1 is equal to the resistance of the second input resistor RS 2 and the resistance of the first resistor R 1 is equal to the resistance of the second resistor R 2 (that is, the resistance of the first floating resistor R 1 ′ is equal to the resistance of the second floating resistor R 2 ′), the common-mode voltage of the differential output signals OUTP and OUTN generated by the transmitter module 20 can be calculated using the following equations.

V′ H is the high level of the differential output signals in the first operation mode, V′ L is the low level of the differential output signals in the first operation mode, V′ CM is the common-mode voltage of the differential output signals in the first operation mode, AVDD sin k is the voltage provided by the second power source VDD 2 , R sin k is the resistance of the first input resistor RS 1 , I DRV is the current value provided by the current source, and R source is the resistance of the first floating resistor R 1 ′ which is equal to 1/N of the resistance of the first resistor R 1 , wherein N is the number of output impedance sub-circuits.

For example, when AVDD sin k =3.3V, R source =R sin k =50 ohm, and I DRV =20 mA:

V′ H =3.05 V,V′ L =2.55 V , and V′ CM =2.8 V.

In other words, when the voltage provided by the second power source VDD 2 is 3.3V, the resistance of the first input resistor R 1 and the resistance of the second resistor R are 50Ω, the resistance of the first floating resistor R 1 ′ and the resistance of the second floating resistor R′ are 50Ω, and current value provided by the current source is 20 mA, then the high level of the differential output signals OUTP and OUTN is 3.05V, the low level thereof is 2.55V, and the common-mode voltage thereof is 2.8V.

Moreover, when the transmitter module 20 operates in the first operation mode, the current I′ source consumed by the transmitter module 20 is equal to zero.

When the first switch K 1 of each output impedance sub-circuit 221 is turned off and the second switch K 2 and the third switch K 3 thereof are turned on, the output resistor provided by the output impedance circuit 21 comprises pull-up resistors, and the transmitter module 20 operates in a second operation mode.

Referring to FIG. 4 , FIG. 4 is a schematic diagram showing an equivalent circuit when the transmitter module shown in FIG. 2 operates in the second operation mode. As shown in FIG. 4 , the first pull-up resistor R 1 ″ and the second pull-up resistor R 2 ″ are the corresponding equivalent resistors of the output impedance circuit 21 .

One terminal of the first pull-up resistor R 1 ″ and one terminal of the second pull-up resistor R 2 ″ are coupled to the first power source VDD 1 . The other terminal of the first pull-up resistor R 1 ″ and the other terminal of the second pull-up resistor R 2 ″ are coupled to the first common node Q 1 and the second common node Q 2 respectively.

When the transmitter module 20 operates in the second operation mode, if the resistance of the first input resistor RS 1 is equal to the resistance of the second input resistor RS 2 and the resistance of the first resistor R 1 is equal to the resistance of the second resistor R 2 (that is, the resistance of the first pull-up resistor R 1 ″ is equal to the resistance of the second pull-up resistor R 2 ″), the common-mode voltage of the differential output signals OUTP and OUTN generated by the transmitter module 20 can be calculated using the following equations.

Moreover, the current consumed by the transmitter module 20 is calculated using the following equations:

I″ source source is the current consumed by the transmitter module in the second operation mode, V″ H is the high level of the differential output signals in the second operation mode, V″ L is the low level of the differential output signals in the second operation mode, V″ CM is the common-mode voltage of the differential output signals in the second operation mode, AVDD source is the voltage provided by the first power source VDD 1 , AVDD source is the voltage provided by the second power source VDD 2 , R sin k is the resistance of the first input resistor RS 1 , I DRV is the current value provided by the current source, and R source is the resistance of the first pull-up resistor R 1 ″ which is equal to 1/N of the resistance of the first resistor R 1 , wherein N is the number of output impedance sub-circuits.

For example, when AVDD source =AVDD sink =3.3V, R source =R sink =50 ohm, and I DRV =20 mA,

V″ H =3.3 V,V″ L =2.8 V , and V″ CM =3.05 V;

I″ source =10 mA

In other words, during the period when the transmitter module 20 operates in the second operation mode, when the voltage provided by the first power source VDD 1 and the voltage provided by the second power source VDD 2 are 3.3V, the resistance of the first input resistor R 1 and the resistance of the second resistor R are 50Ω, the resistance of the first pull-up resistor R 1 ″ and the resistance of the second pull-up resistor R″ are 50Ω, and current value provided by the current source is 20 mA, then the high level of the differential output signals OUTP and OUTN is 3.3V, the low level thereof is 2.8V, the common-mode voltage thereof is 3.05V, and the current consumed by the transmitter module 20 is 10 mA.

When the first switches K 1 of some output impedance sub-circuits 221 are turned on, the second switches K 2 and the third switches K 3 of the some output impedance sub-circuits 221 are turned off, the first switches K 1 of the remaining output impedance sub-circuits 221 are turned off, and the second switches K 2 and the third switches K 3 of the remaining output impedance sub-circuits 221 are turned on, then the output resistor provided by the output impedance circuit 21 comprises floating resistors and pull-up resistors, and the transmitter module 20 operates in a third operation mode.

Referring to FIG. 5 , FIG. 5 is a schematic diagram showing an equivalent circuit when the transmitter module shown in FIG. 2 operates in the third operation mode. As shown in FIG. 5 , the first floating resistor R 1 A, the second floating resistor R 2 A, the first pull-up resistor R 1 B, and the second pull-up resistor R 2 B are the corresponding equivalent resistors of the output impedance circuit 21 .

One terminal of the first floating resistor R 1 A is coupled to one terminal of the second floating resistor R 2 A. The other terminal of the first floating resistor R 1 A and the other terminal of the second floating resistor R 2 A are coupled to the first common node Q 1 and the second common node Q 2 respectively.

One terminal of the first pull-up resistor R 1 B and one terminal of the second pull-up resistor R 2 B are coupled to the first power source VDD 1 . The other terminal of the first pull-up resistor R 1 B and the other terminal of the second pull-up resistor R 2 B are coupled to the first common node Q 1 and the second common node Q 2 respectively.

When the transmitter module 20 operates in the third operation mode, if the resistance of the first input resistor RS 1 is equal to the resistance of the second input resistor RS 2 and the resistance of the first resistor R 1 is equal to the resistance of the second resistor R 2 (that is, the resistance of the first floating resistor R 1 A and the second floating resistor R 2 A are equal to the resistance of the first pull-up resistor R 1 B and the second pull-up resistor R 2 B″), the high level, the low level, and the common-mode voltage of the differential output signals OUTP and OUTN generated by the transmitter module 20 and the consumed current meet the following relationships.

V CM =0.5*( V H +V L )

I source =0˜ I″ source

I source is the current consumed by the transmitter module in the third operation mode, V H is the high level of the differential output signals in the third operation mode, V L is the low level of the differential output signals in the third operation mode, and V CM is the common-mode voltage of the differential output signals in the third operation mode.

In other words, the current I source consumed by the transmitter module in the third operation mode is greater than the current I′ source consumed in the first operation mode (that is 0) and less than the current I″ source consumed in the second operation mode. The common-mode voltage V CM of the transmitter module in the third operation mode is higher than the common-mode voltage V′ CM in the first operation mode and lower than the common-mode voltage V″ CM in the third operation mode.

For example, during the period when the transmitter module 20 operates in the third operation mode, when the voltage provided by the first power source VDD 1 and the voltage provided by the second power source VDD 2 are 3.3V, the resistance of the first input resistor RS 1 and the resistance of the second resistor RS 2 are 50Ω, the sum of the resistance of the first floating resistor R 1 A and the resistance of the first pull-up resistor R 1 B is 50Ω, the sum of the resistance of the second floating resistor R 2 A and the resistance of the second pull-up resistor R 2 B is 50Ω, and current value provided by the current source is 20 mA, then the high level of the differential output signals OUTP and OUTN is 3.05V˜3.3V, the low level thereof is 2.55V˜2.8V, the common-mode voltage thereof is 2.8V˜3.05V, and the current consumed by the transmitter module 20 is 0˜10 mA.

According to the above description, in the first operation mode, the common-mode voltage of the transmitter module 20 is lowest, and the current consumed by the transmitter module 20 is the smallest; in the second operation mode, the common-mode voltage of the transmitter module 20 is highest, and the current consumed by the transmitter module 20 is largest; in the third operation mode, the common-mode voltage and the consumed current are between those of the first operation mode and those of the second operation mode, respectively.

In the embodiments above, the current-mode logic circuit allows the transmitter module to operate in three different operation modes by controlling the states of the first switches, the second switches, and the third switches in the output impedance sub-circuits, so that the common-mode voltage of the differential output signals transmitted by the transmitter module and the current consumed by the transmitter module can be adjusted in response to different operation modes. Thus, the current-mode logic circuit can be flexibly applied to various high-speed transmission applications.

While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.