Patent Application
20240063833
The present invention relates generally to a broadband high power transmit/receive switch system, and a corresponding method.
Time division duplexed (TDD) active antenna systems (AAS) are known in the art for use in, for example, 5G networks (5th generation mobile networks). Active antenna systems (AAS) are used to increase the capacity and coverage of radio streams. Active antenna systems feature a tighter integration of radio frequency (RF) electronics with a multiple-element antenna array to enable miniaturization and to boost efficiency. 5G base stations apply a high number of transmit and receive antenna elements for serving multiple users with parallel data streams. Some active antenna systems include a digital baseband transceiver, an RF frontend, and the multiple-element antenna array. The digital baseband transceiver can include a digital baseband and field-programmable gate array section, a mixed signal section including digital-to-analog converters (DACs) and analog-to-digital converters (ADCs), and a transceiver section for receiving and transmitting RF analog signals. The RF frontend can include driver amplifiers, power amplifiers, variable gain amplifiers, low noise amplifiers, and filters, as well as high voltage RF switching circuitry. In some applications, the RF switching circuitry can experience extremely high RF voltages. To handle these high RF voltages, the switching circuitry must be designed to include multiple stacked transistor stages increasing circuit area and costs. Furthermore, the extremely high RF voltages can lead to premature switching circuit failure.
According to an embodiment, a switch system comprising a first hybrid coupler having a first node coupled to a termination terminal, a second node coupled to an antenna terminal, a third node coupled to a quadrature terminal, and a fourth node coupled to an in-phase terminal; and a radio frequency (RF) switch having a first switch coupled between the quadrature terminal and ground, and a second switch coupled between the in-phase terminal and ground, wherein the termination terminal is configured for coupling to a load, wherein the load and the RF switch dissipate RF power due to a transmit mode insertion loss, and wherein a majority of the RF power is reflected into the load by the first hybrid coupler.
A method of operating a switch system, the switch system including a hybrid coupler having a first node configured for coupling to a load, a second node configured for coupling to an antenna, a third node, and a fourth node; and a radio frequency (RF) switch having a first switch coupled between the third node and ground, and a second switch coupled between the fourth node and ground, the method comprising turning off the first switch and the second switch such that RF power is dissipated in the load and the RF switch due to a transmit mode insertion loss, and such that a majority of the RF power is reflected into the load.
A receive path for a radio frequency (RF) frontend comprising a hybrid coupler having a first input configured for coupling to a load, a second input configured for coupling to an antenna, a first output, and a second output; an RF switch configured for selectively coupling the first output and the second output to ground; and a low noise amplifier circuit coupled to the RF switch, wherein the load and the RF switch dissipate RF power due to a transmit mode insertion loss, and wherein a majority of the RF power is dissipated by the hybrid coupler.
For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.
In the following detailed description, reference is made to the accompanying drawings, which form a part hereof and in which are shown by way of illustrations specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. For example, features illustrated or described for one embodiment can be used on or in conjunction with other embodiments to yield yet a further embodiment. It is intended that the present invention includes such modifications and variations. The examples are described using specific language, which should not be construed as limiting the scope of the appending claims. The drawings are not scaled and are for illustrative purposes only. For clarity, the same or similar elements have been designated by corresponding references in the different drawings if not stated otherwise.
According to the embodiment of
In an embodiment, the hybrid coupler is tuned to an operating RF frequency of interest. Hybrid couplers are the special case of a four-port directional coupler that is designed for a 3-dB (equal) power split. Hybrids couplers come in two types, 90 degree or quadrature hybrids, and 180 degree hybrids. In embodiments, the components of the hybrid couplers are designed to provide a quadrature hybrid coupler at the frequency of interest.
In an embodiment, the first hybrid coupler 302 comprises two coupled lines of a multi-layer laminated hybrid, the RF switch 304 comprises an integrated circuit affixed to the multi-layer laminated hybrid, and the low noise amplifier circuit 306 comprises one or more integrated circuits and optional external components.
A lumped-model equivalent circuit 312 of the two coupled lines of the first hybrid coupler 302 includes inductor L3 and inductor L4, capacitor C3 coupled between a first end of inductor L3 and a second end of inductor L4, and capacitor C4 coupled between a first end of inductor L4 and a second end of inductor L3. Further components of the first hybrid coupler 302 includes parasitic inductor L1 coupled to the first end of inductor L3, parasitic inductor L2 coupled to the first end of inductor L4, parasitic inductor L5 coupled to the second end of inductor L3, and parasitic inductor L6 coupled to the second end of inductor L4. The first hybrid coupler 302 further comprises capacitor C1 coupled between terminal 308 and ground, capacitor C2 coupled between terminal 310 and ground, capacitor C5 coupled between terminal 314 and ground, and capacitor C6 coupled between terminal 316 and ground. These parasitic components model the package parasitics of the hybrid, in an embodiment. Capacitors C1, C2, C5, and C6 are capacitances for tuning the RF characteristics of the first hybrid coupler 302.
Switch system 300A of
In some embodiments, the RF switch 304 comprises a third switch S3 also coupled between the in-phase terminal 314 and ground, and a fourth switch S4 also coupled between the quadrature terminal 316 and ground. The parallel configuration of switches S1 and S2, and S3 and S4 are used in some embodiments for greater reliability and high input power handling ability. Quality is improved by sharing the high input power handling between two switches. Switches S1 and S2 are switched together and switches S3 and S4 are also switched together. The operation and control of switches S1, S2, S3, and S4 is described in further detail below. RF switch also includes DC blocking capacitors C7 coupled between terminals 314 and 318 and C8 coupled between terminals 316 and 320. DC blocking capacitors C7 and C8 can be omitted in some embodiments depending on the design of the low noise amplifier circuit 306.
Switch system 300A of
In an embodiment, inductors L7, L8, L9, and L10 are non-parasitic inductors. Inductors L7 and L8 are used for parasitic capacitance compensation of the input capacitance of RF switch 304. In particular, inductors L7 and L8 are used to compensate the Coff capacitance of RF switch 304 and to provide improved ESD protection. In an embodiment, inductors L7 and L8, and the Coff capacitance of RF switch 304 creates a resonant tank circuit at the RF frequency of interest (high AC impedance). Inductors L9 and L10 are used to match the input capacitance of the low noise amplifier circuit 306. Adjusting component values using matching techniques are known in the art, for example using a Smith Chart or using RF matching software. In some embodiments, a noise match is made in order to decrease the noise figure of the system, even though the resulting match may result in some reflection.
In an embodiment, low noise amplifier circuit 306 comprises low noise amplifier 326 having an input coupled to terminal 322 and a low noise amplifier 328 coupled to terminal 324. The outputs of low noise amplifier 326 and low noise amplifier 328 are coupled to a second hybrid coupler 327 including inductor L11 and inductor L12, capacitor C9 coupled between a first end of inductor L11 and a second end of inductor L12, and capacitor C10 coupled between a first end of inductor L12 and a second end of inductor L11. Inductors L11 and L12, and capacitors C9 and C10 represent a lumped element model of the second hybrid coupler 327. Low noise amplifier circuit 306 further comprises low noise amplifier 330 selectively coupled between the second hybrid coupler 327 through switches S5, S6, and S7 and the RX output at terminal 332. When additional gain from low noise amplifier 330 is required switches S5 and S6 are open and switch S7 is closed. When additional gain is not required, switches S5 and S6 are closed and switch S7 is open to bypass low noise amplifier 330. The second hybrid coupler 327 can comprise an on-chip hybrid on the one or more low noise amplifier integrated circuits. In some embodiments the second hybrid coupler can comprise a discrete Surface Mount Device (SMD) implementation using separate inductors and capacitors, or an implementation similar to that used for the first hybrid coupler 302 (multi-layer laminate hybrid). The second hybrid coupler 327 is “matched” to the first hybrid coupler 302 as is explained in further detail below.
In the receive mode of operation, the ANT signal at terminal 308 is split into the I/Q signal at terminals 314 and 316. These signals pass through RF switch 304 (i.e., switches S1, S2, S3, and S4 are open) and be routed to the inputs of low noise amplifier 326 and low noise amplifier 328. Low noise amplifier 326 and low noise amplifier 328 amplify the I/Q signal. The second hybrid coupler 327 sums the amplified I/Q signal into a single-ended signal. This single-ended signal will be either amplified by low noise amplifier 330 or directly routed to the RX terminal 332 as explained above. The first hybrid coupler 302 (specifically the equivalent circuit 312) is “matched” with the second hybrid coupler 327. The term “matched” is defined herein as both hybrid couplers 302 and 327 having the same amplitude and phase characteristics. The matched hybrid couplers advantageously results in the noise at the TERM terminal 308 being cancelled.
In operation, the input RF current into the antenna terminal is reflected back through the termination terminal 308 and the antenna terminal 310 with a split ratio of approximately 0.5. By placing the first hybrid coupler 302 in front of RF switch 304 at least 90% of the input RF power is dissipated in the first hybrid coupler 302 and less than 3% of the input RF power is dissipated in the RF switch 304.
In
I_IN*a*sQ(Θ°−α); and [1]
I_IN*a*sI(0°−α), wherein [2]
It is important to note that switches S1, S2, S3, and S4 of the RF switch 304 are shown as short circuits in the transmit mode equivalent circuit of
The input current at the ANT terminal 310 is I_IN, the reflected current at the ANT terminal 310 is I_OUT_ANT, and the reflect current at the TERM terminal 308 is I_OUT_TERM. The current components at the output of first hybrid coupler 302 include I_IN_I, which is the in-phase signal from the first hybrid coupler 302 and is described by equation [2] set forth above, I_IN_I_B, which is the back-scattered in=phase signal from the first hybrid coupler 302, I_IN_Q, which is the quadrature phase signal from the first hybrid coupler 302 and is described by [1] set forth above, and I_IN_Q_B, which is the back scattered quadrature phase signal from the first hybrid coupler 302.
The input current components to the RF switch 304 include I_IN_Q_F, which is the forward-scattered quadrature phase signal from the first hybrid coupler 302, and I_IN_I_F, which is the forward scattered in-phase signal from the first hybrid coupler 302. Current components I_IN_Q_F and I_IN_I_F are respectively described by the following:
I_IN*a*sQ*(1−Γ_rx)(Θ°−α); and [3]
I_IN*a*sI*(1−Γ_rx)(0°−α). [4]
The output current components from the RF switch 304, which are also current components to the inputs of the low noise amplifier circuit 306, are labeled I_IN_I_LNA_IN and I_IN_Q_LNA_IN. I_IN_I_LNA_IN is the forward-scattered in-phase signal from the first hybrid coupler 302 into LNA circuit 306 in the in-phase path and is approximately equal to I_IN_I, previously defined. I_IN_Q_LNA_IN is the forward-scattered quadrature phase signal from the first hybrid coupler 302 into LNA circuit 306 in the quadrate path and is approximately equal to I_IN_Q, previously defined.
The output current components from the LNA circuit 306 are labeled, from the top of
I_IN_Q_LNA_OUT_Q˜I_IN*a*b*sQ*sI2((Θ+0)°−α−β); [5]
I_IN_Q_LNA_OUT_I˜I_IN*a*b*sI*sQ2((0+ϕ)°−α−β); [6]
I_IN_I_LNA_OUT_Q˜I_IN*a*b*sQ*sQ2((Θ+ϕ)°−α−β); and [7]
I_IN_I_LNA_OUT_I˜I_IN*a*b*sI*sI2((0)*−α−β), [8]
wherein, with respect to [3], [4], [5], [6], [7], and [8]:
Finally, the output currents of the RF switch system 300C in
I_OUT_TERM=I_IN*a*sQ*Γ_rx*(2*Θ°−2*α)+I_IN*a*sI*Γ_rx*(2*Θ°−2*α) [9]
I_OUT_ANT=I_IN*a*sQ*Γ_rx*(0°−2*α)+I_IN*a*sI*Γ_rx*(2*Θ°−2*α) [10]
I_OUT_RX˜I_IN*a*b*sQ*sI2*((Θ+0)°−α−β)+I_IN*a*b*sI*sQ2*((0+Φ)°−α−β) [11]
for sI=sQ and Θ=90° with respect to equations [9] and [10], and for sQ=sI=sQ2=sI2=0.5, a=b=1, and Θ=Φ with respect to equation [11].
The following description is related to noise cancellation in the RF switch system of the present invention, according to embodiments.
From an outside observer at the ANT port 310, any reflections at the noise matched LNA lineup reference plane at Γ_rx will be scattered back to the first hybrid coupler 302 and will be terminated at the load resistor in the TERM port 308. As such, the observer at the ANT port 310 will not detect a back-scattered wave at the ANT port 310. This is by definition a perfect noise match at the ANT port 310.
Inside the hybrid island of hybrid coupler 302, the LNA will be optimized for the best noise figure (NF), which is not a perfect match, but best for NF. Since reflections will propagate to the TERM port 308 and not the ANT port 310, the match seen from the ANT port 310 is still perfect. Just the Γ_rx based gain drop at each chain (I and Q path) will be slightly lower than the available power gain of the LNA lineup.
At the TERM port 308, there is a termination resistor R TERM 130 with the value of Zo (e.g. a 50 Ohm characteristic Impedance). Such a resistive device typically has a thermal noise voltage which can be converted to a thermal noise current. This noise current will propagate from TERM port 308 of the first hybrid 302 to the TERM port (input of LNA2) of the second hybrid 327 with the same equation as the input signal current I_IN at the ANT port 310 of the first hybrid to the input of LNA2 330.
Example embodiments of the present invention are summarized here. Other embodiments can also be understood from the entirety of the specification and the claims filed herein.
While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.
This application claims the benefit of U.S. Provisional Application No. 63/371,574, filed on Aug. 16, 2022, and to co-pending U.S. application Ser. No. ______ (not yet assigned) filed on the same day as this application, entitled “BROADBAND TRX HYBRID IMPLEMENTATION” and associated with Attorney Docket No. INF 2022 P 07356 US01, both of which applications are hereby incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63371574 | Aug 2022 | US |
