Directional couplers are devices that detect signal power being transmitted in a particular direction. Directional couplers are used to detect signal in a wide variety of radio frequency circuits. A directional coupler includes four ports. The first port is an input port that receives a transmitted signal from a source. The second port is an output port that provides the transmitted signal to a destination, As signal propagates from the first port to the second port, a portion of the signal is coupled to the third port. The third port is a coupled port that outputs signal coupled from the transmitted signal. The fourth port is an isolated port. Preferably, no signal is coupled to the fourth port. Output of the third port may be applied to measure or control the power of the transmitted signal, or to determine parameters of the transmission signal path.
Directional couplers that provide independent control of magnetic and capacitive coupling are described herein. In one example, an on-chip directional coupler includes a first linear conductive trace, a second linear conductive trace, a first curved conductive trace, and a second curved conductive trace. The first linear conductive trace is formed in a first metal layer, and includes an end and a coupled port. The second linear conductive trace is formed in the first metal layer, and is spaced apart from and parallel to the first linear conductive trace. The second linear conductive trace includes an end and an isolated port. The first curved conductive trace is formed in a second metal layer, and includes a first end and a second end. The first end is conductively coupled to the end of the of the first linear conductive trace. The second curved conductive trace is formed in the first metal layer, and includes a first end and a second end. The first end of the second curved conductive trace is conductively coupled to the second end of the first curved conductive trace. The second end of the second curved conductive trace is conductively coupled to the end of the second linear conductive trace.
In another example, an on-chip directional coupler includes a first linear conductive trace, a second linear conductive trace, and a conductive loop. The first linear conductive trace including an end and a coupled port. The second linear conductive trace is spaced apart from and parallel to the first linear conductive trace. The second linear conductive trace includes an end and an isolated port. The conductive loop includes a first end conductively coupled to the end of the first linear conductive trace, and a second end conductively coupled to the end of the second linear conductive trace.
In a further example, an integrated circuit includes a transmit power amplifier, a transmission conductor, a transmit terminal, and a directional coupler. The transmit power amplifier including an output. The transmission conductor includes a first end and a second end. The first end of the transmission conductor is conductively coupled to the output of the transmit power amplifier. The transmit terminal is conductively coupled to the second end of the transmission conductor. The directional coupler is configured to detect signal in the transmission conductor, and includes a first linear conductive trace, a second linear conductive trace, and a conductive loop. The first linear conductive trace is formed in a first metal layer and includes an end and a coupled port. The second linear conductive trace is formed in the first metal layer, and is spaced apart from and parallel to the first conductive trace. The second linear conductive trace includes an end and an isolated port. The conductive loop is formed in the first metal layer and a second metal layer, and includes a first end and a second end. The first end of the conductive loop is conductively coupled to the end of the first linear conductive trace. The second end of the conductive loop is conductively coupled to the end of the second linear conductive trace.
Radio frequency (RF) integrated circuits, such as automotive radar integrated circuits, include built-in self-test systems the employ on-chip directional couplers to verify signal path components and connections. Conventional on-chip directional couplers suffer from interdependency of parameters that result in performance compromises, such as large circuit area or low directivity.
The ground plane 114 and the ground plane 116 isolate the conductive signal trace 102 and the conductive coupling trace 108 from noise sources in the integrated circuit. The ground plane 114 and the ground plane 116 may be formed on the same metal layer as the conductive signal trace 102 and the conductive coupling trace 108, and/or on a metal layer other than that of the conductive signal trace 102 and the conductive coupling trace 108.
The loading trace segments 118 are provided on a metal layer of the integrated circuit other than that of the conductive signal trace 102 and the conductive coupling trace 108. The loading trace segments 118 load the conductive signal trace 102 and the conductive coupling trace 108 to help control parasitic capacitance.
Z0=√{square root over (ZeZo)}
where: Ze is even mode impedance; and Zo is odd mode impedance.
Even mode impedance is:
Odd mode impedance is:
The ratio of even mode impedance to odd mode impedance is:
The ratio of odd mode propagation constant (βo) to even mode propagation constant (βe) is:
In equations (2)-(5), because k, Cp, and CCare not independent, even and odd mode impedance and propagation constant cannot be set independently to achieve low coupling and high directivity.
The directional coupler 300 includes a signal conductor 302 and a coupling conductor 304. The signal conductor 302 includes an input port 302A and an output port 302B. The coupling conductor 304 includes a coupled port 304A and an isolated port 304B. Signal introduced to the signal conductor 302 via the input port 302A exits the signal conductor 302 at the output port 302B. As signal traverses the signal conductor 302, a portion of the signal is magnetically and/or capacitively coupled into the coupling conductor 304, and exits the coupling conductor 304 via the coupled port 304A.
The coupling conductor 304 includes a linear conductive trace 306, a linear conductive trace 308, and a conductive loop 305. A first end of the linear conductive trace 306 is conductively coupled to the coupled port 304A, and a second end 306A of the linear conductive trace 306 is conductively coupled to the conductive loop 305. A first end of the linear conductive trace 308 is conductively coupled to the isolated port 304B, and a second end 308A of the linear conductive trace 306 is conductively coupled to the conductive loop 305. The linear conductive trace 306, the linear conductive trace 308, and the conductive loop 305 form a transformer-like structure that allows for control of magnetic coupling in the directional coupler 300 (magnetic coupling between the signal conductor 302 and the coupling conductor 304) as a function of (a ratio of) diameter (dm) of the conductive loop 305 to length (dp) of the linear conductive trace 306 and linear conductive trace 308. As shown in
The linear conductive trace 306 and the linear conductive trace 308 are formed in a same metal layer of the integrated circuit. A first portion of the conductive loop 305 is formed in the same (a first) metal layer as the linear conductive trace 306 and the linear conductive trace 308, and second portion of the conductive loop 305 is formed in a different (a second) metal layer of the integrated circuit. The conductive loop 305 includes a first curved conductive trace 316, and a second curved conductive trace 318. The second curved conductive trace 318 is formed in the same metal layer as the linear conductive trace 306 and the linear conductive trace 308 (first metal layer). The first curved conductive trace 316 is formed in a different metal layer (second metal layer) than the second curved conductive trace 318. The first curved conductive trace 316 includes a first end 316A and a second end 316B. The second curved conductive trace 318 includes a first end 318A and a second end 318B. The first end 316A of the first curved conductive trace 316 is coupled to the first end 318A of the second curved conductive trace 318 by a via 310 that connects the metal layers of the first curved conductive trace 316 and the second curved conductive trace 318. Similarly, the second end 316B of the first curved conductive trace 316 is coupled to the second end 308A of the linear conductive trace 308 by a via 312 that connects the metal layers of the first curved conductive trace 316 and the linear conductive trace 308. The second end 318B of the second curved conductive trace 318 is coupled to the second end 306A of the linear conductive trace 306.
The first curved conductive trace 316 includes a conductive trace segment 320 that is coupled to the linear conductive trace 308, and may be perpendicular to the linear conductive trace 306 and the linear conductive trace 308. The second curved conductive trace 318 includes a conductive trace segment 322, a conductive trace segment 324, and a conductive trace segment 326. The conductive trace segment 322 may be perpendicular to the linear conductive trace 306 and the linear conductive trace 308. The conductive trace segment 326 is coupled to, and may be perpendicular to, the conductive trace segment 322. The conductive trace segment 324 is coupled to, and may be perpendicular to, the conductive trace segment 326.
The signal conductor 302 may be formed in the same metal layer as the first curved conductive trace 316, the same metal layer as the second curved conductive trace 318, or a different metal layer. The coupling capacitance between the signal conductor 302 and the coupling conductor 304 may be reduced by placing the signal conductor 302 on a different metal layer from the linear conductive trace 306 and the linear conductive trace 308. A ground plane 328 isolates the signal conductor 302 and the coupling conductor 304 from other circuitry of the integrated circuit.
By providing independent control of magnetic coupling, the directional coupler 300 provides improved directivity (e.g., 3 decibels (dB) improvement) in a significantly smaller (e.g., 60% smaller) area than conventional directional couplers.
The conductive loop 705 may be provided in various shapes. For example, the conductive loop 705 may be rectangular, octagonal, circular, etc. Similarly, the shape of the signal conductor 702 surrounding the conductive loop 705 may be provided in various shapes (e.g., rectangular, octagonal, circular, etc.). The shape of the signal conductor 702 surrounding the conductive loop 705 may be the same as or different from the shape of the conductive loop 705.
In some implementations of the integrated circuit 800, the directional coupler 804 is designed to in conjunction with packaging of the integrated circuit 800 so that package capacitance is included in the design of the directional coupler. By including package capacitance in the parasitic capacitance of the directional coupler 804, transmitted signal loss may be reduced relative to designs employing a shunt stub to resonate out package capacitance.
The term “couple” is used throughout the specification. The term may cover connections, communications, or signal paths that enable a functional relationship consistent with the description of the present disclosure. For example, if device A generates a signal to control device B to perform an action, in a first example device A is coupled to device B, or in a second example device A is coupled to device B through intervening component C if intervening component C does not substantially alter the functional relationship between device A and device B such that device B is controlled by device A via the control signal generated by device A.
Modifications are possible in the described embodiments, and other embodiments are possible, within the scope of the claims.
What is claimed is: