DESC:TECHNICAL FIELD
[0001] The present disclosure relates generally to a power amplifier. The disclosure more particularly relates to a gallium nitride (GaN) power amplifier.

BACKGROUND
[0002] Power Amplifiers are one of the major components of Transmit/Receive modules which are targeted for efficiency improvement due to the large output power generated. Tx/Rx modules with highly integrated devices enable beam-forming and steering, form the heart of Active Phased Array Radars. Size, weight and power (SWaP) are the key criteria in these RADAR and communication platforms.
[0003] To meet such requirements, GaN based HEMTs are well suited as they are characterized by high power density, high breakdown voltage, moderate gain and high efficiency. Internally matched FET topology offers better features in compact form-factor in comparison to bulky PAs with unmatched transistors.
[0004] US Patent No. 6,281,756 B1 dated August 28, 2001, discloses an internally impedance matched transistor circuit in a package for preventing low frequency oscillation during high frequency band operation by disposing an oscillation-preventing stabilization circuit comprising a resistor connected to ground through a capacitor.
[0005] Korean Patent no. 102224203B1 discloses a realization technique for broadband Class J PA using internally matched configuration in S-Band. However, the gain realized <10 dB and the form factor is large.
[0006] The paper “GaN X-band 43% Internally-Matched FET with 60W Output Power” discuss about X band Internally matched PA delivering 60.3 watt with 43.4% PAE. Asymmetric matching circuit layout is employed to avoid decrease of efficiency caused by impedance mismatch and unbalance power dividing in matching circuits. However, it combines multiple FETs and is not packaged.
[0007] The paper “An S-band Internally Matched Packaged GaN HEMT with over 720W Peak Power and 58% PAE” (Published in IEEE/MTT-S International Microwave Symposium, 2018) discuss about S band internally matched GaN HEMT PA delivering 720 Watt peak with 58% PAE. However, impedance matching networks has been fabricated using aluminium nitride substrates and packaged in 24 mmX17.4 mm. The operating frequency range is a narrow band of 3.2-3.6GHz, power gain of 9.8dB.
[0008] While the above cited references introduce and disclose GaN HEMT based Power Amplifiers, it is felt that a focused solution for miniaturized, high gain S-Band Power Amplifier in a metal package for excellent thermal management is not available.
SUMMARY
[0009] This summary is provided to introduce concepts of the invention related to a single chip gallium nitride (GaN) power amplifier, as disclosed herein. This summary is neither intended to identify essential features of the invention as per the present invention nor is it intended for use in determining or limiting the scope of the invention as per the present invention.
[0010] In accordance with an embodiment of the present invention, a single chip S-band Gallium Nitride (GaN) power amplifier is provided. The power amplifier comprising: an input matching network configured to receive an external radio frequency (RF) input signal and match the 50 Ohm RF impedance to a predefined input impedance; an input shunt capacitor configured to block DC signal from the RF input signal; a single stage amplifier connected the input shunt capacitor and configured to amplify power of the RF input signal; an output shunt capacitor connected to the single stage amplifier and configured to block DC signal from the amplified RF signal; and an output matching network connected to the output shunt capacitor and configured to match power of the amplified RF signal to a predefined output impedance.
[0011] In an embodiment, said amplifier is fabricated on a 4.4 mm thick aluminium substrate with a die size of 20.6 X 14.6 mm.
[0012] In an embodiment, said single stage amplifier has a gallium nitride-based high electron mobility transistor (GaN HEMT) fabricated on a 0.4 µm thick GaN (Gallium Nitride) substrate having physical dimension of 1 X 6 mm.
[0013] In an embodiment, the amplifier has thermal resistance of 0.64 degree Celsius per Watt.
[0014] In an embodiment, the input shunt capacitor and the output shunt capacitor are variable to optimize matching for power, efficiency, and bandwidth of the amplifier.
[0015] In an embodiment, said GaN HEMT has power gain of 12dB and is configured to deliver 150-watt output power.
[0016] In an embodiment, said predefined output impedance is 50 Ohms.
[0017] In an embodiment, a gold bond-wire is used for interconnection between the output shunt capacitor, the output matching network, and the output RF pin.
[0018] In an embodiment, the amplifier has <0.3 dB power droop across temperature with 20% duty cycle, and <0.3 dB power gain variation across temperature.
[0019] In an embodiment, the operating frequency range of the amplifier is 2.7 GHz to 3.6 GHz.
[0020] In an embodiment, the amplifier has drain efficiency of >50%.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
[0021] The detailed description is described with reference to the accompanying figures.
[0022] Figure 1 illustrates a functional block diagram of an S-band GaN power amplifier, according to an exemplary implementation of the present disclosure.
[0023] It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative methods embodying the principles of the present disclosure. Similarly, it will be appreciated that any flow charts, flow diagrams, and the like represent various processes which may be substantially represented in computer readable medium and so executed by a computer or processor, whether or not such computer or processor is explicitly shown.

DETAILED DESCRIPTION
[0024] The present disclosure describes single stage, high gain internally matched S-band GaN power amplifier.
[0025] In the following description, for purpose of explanation, specific details are set forth in order to provide an understanding of the present disclosure. It will be apparent, however, to one skilled in the art that the present disclosure may be practiced without these details. One skilled in the art will recognize that embodiments of the present disclosure, some of which are described below, may be incorporated into a number of systems.
[0026] However, the systems and methods are not limited to the specific embodiments described herein. Further, structures and devices shown in the figures are illustrative of exemplary embodiments of the presently disclosure and are meant to avoid obscuring of the presently disclosure.
[0027] It should be noted that the description merely illustrates the principles of the present invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present invention. Furthermore, all examples recited herein are principally intended expressly to be only for explanatory purposes to help the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass equivalents thereof.
[0028] In one of the embodiment, the S-band Gallium Nitride (GaN) power amplifier discloses herein is a single chip power amplifier comprising: an input matching network configured to receive an external radio frequency (RF) input signal and match the 50 Ohm RF impedance to a predefined input impedance; an input shunt capacitor configured to block DC signal from the RF input signal; a single stage amplifier connected the input shunt capacitor and configured to amplify power of the RF input signal; an output shunt capacitor connected to the single stage amplifier and configured to block DC signal from the amplified RF signal; and an output matching network connected to the output shunt capacitor and configured to match power of the amplified RF signal to a predefined output impedance.
[0029] The single stage, internally matched, high gain, GaN-on-SiC HEMT based high power amplifier is configured to deliver 150W saturated output power in S-Band. The drain efficiency is >50% and it has a high single stage gain of ~12dB. Input and output matching networks based on Alumina substrate are interconnected with customized SLCs and a GAN HEMT fabricated on 0.4um, 8-10W power density process and encapsulated in a metal package in a compact form factor of 20.6mmX14.6mm. The gate periphery of the transistor is optimized to obtain high single stage gain. Tunable external single layer capacitor is provided on gate and drain side to optimize matching for power, efficiency and bandwidth.
[0030] In an embodiment, the present disclosure the single stage internally matched GaN Power amplifier comprising an input matched network (101), input customized SLC capacitor (102), output customized SLC capacitor (104), output matched network (105) and GaN HEMT (103) fabricated on 0.4 um GaN pHEMT process having the following features: Power gain of 12 dB delivering 150-watt output power; Drain efficiency of >50%; Wideband operation of 2.7-3.6 GHz; Power drop of <0.3 dB across temperature with 20% duty cycle (Pulse width:1 msec); <0.3 dB variation in Power gain across Temperature; Operating temperature of -40ºC to +55ºC.
[0031] In an embodiment, the GaN HEMT with physical dimensions of ~1mm X ~6mm and customized gate periphery having 80 fingers on 0.4um GaN process to obtain high single stage gain of ~12 dB in S-Band.
[0032] In an embodiment, the metal flange package with dimensions of 20.6mm X 14.6mm and thermal resistance~0.64 ºC/W to encapsulate input & output matching networks on Alumina substrate with customized Single layer capacitors and GaN HEMT with periphery of 6mm2.
[0033] In an embodiment, the amplifier includes a tunable external capacitor on gate and drain side to optimize matching for power, efficiency, and bandwidth.
[0034] In an embodiment, referring to figure 1, the present disclosure discloses a design and development of Internally matched S-Band 150W Metal Packaged GaN Power Amplifier (100) realized using 0.4um GaN HEMT technology. The Power Amplifier (100) has an input (RFIN) and an output (RFOUT) terminals and comprises of the following components: Input matching network (101); Input DC blocking capacitor (102); GaN HEMT (103); Output matching network (104); Output DC blocking capacitor (105). the input matching network configured to receive an external radio frequency (RF) input signal and match the 50 Ohm RF impedance to a predefined input impedance; the input shunt capacitor configured to block DC signal from the RF input signal; the single stage amplifier connected the input shunt capacitor and configured to amplify power of the RF input signal; the output shunt capacitor connected to the single stage amplifier and configured to block DC signal from the amplified RF signal; and the output matching network connected to the output shunt capacitor and configured to match power of the amplified RF signal to a predefined output impedance.
[0035] The power amplifier, GaN HEMT (103) is fabricated on a 0.4um, 8-10W/mm power density process with a periphery of 6mm2. The gate width and gate fingers have been optimized to obtain high gain from a single stage and output power of 150W. The input matching network (101) has been designed for 1 GHz bandwidth on Alumina substrate for compact size of ~3.7mm X 7.7mm.
[0036] A customized input DC blocking capacitor (102) has been fabricated to block DC signal and is a part of matching network too. Also, size of capacitor aids in low defect bonding between the capacitor (102) and GaN HEMT (103) and capacitor (102) & input matching network (101). The drain of the GaN HEMT (103) is connected to the output DC blocking capacitor (104) whose value has been customized and fabricated to aid in output matching. The output matching network (105) has been realized on Alumina substrate in compact size. The interconnection between GaN HEMT (103), Output DC blocking Capacitor (104) Output matching network upto RFOUT pin is through gold bond-wires.
[0037] The Power Amplifier (100) is unconditionally stabilized using RC parallel network at gate side. Thermal management is critical for GaN High Power Amplifiers. In this work, the GaN HEMT junction temperature was characterized (Theta JC- Junction to Case). At 150W saturated output power, the resulting (Theta JC) was measured and estimated to be around ~1.2ºC/W. A compact metal package was selected with theta JC ~0.64 ºC/W to optimize thermal dissipation.
[0038] In an embodiment, the Amplifier is a Single stage broadband GaN HEMT based Hybrid power amplifier operated in the frequency range of 2.7 – 3.6 GHz. It features high gain of 12 dB power gain at output power of 51.8 dBm. The amplifier is a 50 Ohm matched, DC Decoupled design with Metalic flange package for better thermal conductivity and moisture protection. Package Dimensions are 16.6 x 14.6 x 4.4 mm. The Power amplifiers are ROHS complaint.
[0039] In an embodiment, the present disclosure provides a single chip S-band Gallium Nitride (GaN) power amplifier (100) comprising: an input matching network (101) configured to receive an external radio frequency (RF) input signal and match the 50 Ohm RF impedance to a predefined input impedance; an input shunt capacitor (102) configured to block DC signal from the RF input signal; a single stage amplifier (103) connected the input shunt capacitor (102) and configured to amplify power of the RF input signal; an output shunt capacitor (104) connected to the single stage amplifier (103) and configured to block DC signal from the amplified RF signal; and an output matching network (105) connected to the output shunt capacitor and configured to match power of the amplified RF signal to a predefined output impedance.
[0040] The amplifier (100) is fabricated on a 4.4 mm thick aluminium substrate with a die size of 20.6 X 14.6 mm.
[0041] The amplifier (100) comprising a single stage amplifier (102) has a gallium nitride-based high electron mobility transistor (GaN HEMT) fabricated on a 0.4 µm thick GaN (Gallium Nitride) substrate having physical dimension of 1 X 6 mm.
[0042] The amplifier (100) has thermal resistance of 0.64 degree Celsius per Watt.
[0043] The amplifier (100) comprising the input shunt capacitor (102) and the output shunt capacitor (104) are variable to optimize matching for power, efficiency, and bandwidth of the amplifier (100).
[0044] The GaN HEMT (103) has power gain of 12dB and is configured to deliver 150-watt output power.
[0045] The predefined output impedance is 50 Ohms.
[0046] In the amplifier (100) a gold bond-wire is used for interconnection between the output shunt capacitor (104), the output matching network (105), and the output RF pin.
[0047] The amplifier (100) has <0.3 dB power droop across temperature with 20% duty cycle, and <0.3 dB power gain variation across temperature.
[0048] An operating frequency range of the amplifier (100) is 2.7 GHz to 3.6 GHz.
[0049] The amplifier (100) has drain efficiency of >50%.
[0050] At least some of the technical advancements of the above disclosed single chip X-band power amplifier (100) include the following:
Internally matched 0.4um GaN HEMT based Power with typical Power Gain of 12 dB and delivering 150W Output Power and packaged in a metal package in compact form factor;
Broad Operating frequency range of 2.7-3.6 GHz;
Drain Efficiency >50% across the band;
Input and Output Matching networks realized on compact Alumina substrates;
<0.3 dB variation in Power across Temperature;
Input and Output matching network can be fine-tuned to shift RF operating frequency to a certain extent.
[0051] The proposed solution addresses the problem of the prior arts by use of 0.4um GaN on SiC HEMTs which are internally matched on alumina substrates in a metal package in a compact form factor with excellent thermal handling capabilities.
[0052] The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the substance of the invention may occur to person skilled in the art, the invention should be construed to include everything within the scope of the invention.
,CLAIMS:

1. A single chip S-band Gallium Nitride (GaN) power amplifier (100) comprising:
an input matching network (101) configured to receive an external radio frequency (RF) input signal and match the 50 Ohm RF impedance to a predefined input impedance;
an input shunt capacitor (102) configured to block DC signal from the RF input signal;
a single stage amplifier (103) connected the input shunt capacitor (102) and configured to amplify power of the RF input signal;
an output shunt capacitor (104) connected to the single stage amplifier (103) and configured to block DC signal from the amplified RF signal; and
an output matching network (105) connected to the output shunt capacitor and configured to match power of the amplified RF signal to a predefined output impedance.

2. The amplifier (100) as claimed in claim 1, wherein said amplifier (100) is fabricated on a 4.4 mm thick aluminium substrate with a die size of 20.6 X 14.6 mm.

3. The amplifier (100) as claimed in claim 1, wherein said single stage amplifier (102) has a gallium nitride-based high electron mobility transistor (GaN HEMT) fabricated on a 0.4 µm thick GaN (Gallium Nitride) substrate having physical dimension of 1 X 6 mm.

4. The amplifier (100) as claimed in any one of claims 1 to 3, wherein the amplifier (100) has thermal resistance of 0.64 degree Celsius per Watt.

5. The amplifier (100) as claimed in claim 1, wherein the input shunt capacitor (102) and the output shunt capacitor (104) are variable to optimize matching for power, efficiency, and bandwidth of the amplifier (100).

6. The amplifier (100) as claimed in claims 1, wherein said GaN HEMT (103) has power gain of 12dB and is configured to deliver 150-watt output power.

7. The amplifier (100) as claimed in claim 1, wherein said predefined output impedance is 50 Ohms.

8. The amplifier (100) as claimed in claim 1, wherein a gold bond-wire is used for interconnection between the output shunt capacitor (104), the output matching network (105), and the output RF pin.

9. The amplifier (100) as claimed in claim 1, wherein the amplifier (100) has <0.3 dB power droop across temperature with 20% duty cycle, and <0.3 dB power gain variation across temperature.

10. The amplifier (100) as claimed in claim 1, wherein operating frequency range of the amplifier (100) is 2.7 GHz to 3.6 GHz.

11. The amplifier (100) as claimed in claim 1, wherein the amplifier has drain efficiency of >50%.