Single package multi-chip RF power amplifier

[0002] This application is related to application Ser. No. 10/059,866, filed Jan. 28, 2002, for N-WAY RF POWER AMPLIFIER WITH INCREASED BACKOFF POWER AND POWER ADDED EFFICIENCY, now U.S. Pat. No. 6,700,444, assigned to the present Assignee, and incorporated herein for all purposes.

[0003] This invention relates generally to a multi-chip RF power amplifier, and more particularly the invention relates to packaging a multi-chip RF power amplifier.

[0004] Semiconductor power amplifiers typically comprise a plurality of semiconductor chips with each chip embodying a transistor amplifier, such as a silicon laterally diffused MOS field effect transistor (LDMOSFET). The transistor amplifiers can be operated in parallel to provide an increased power amplifier output, or the transistor amplifiers can comprise a main or carrier amplifier for maximum back-off power operation and a plurality of auxiliary or peak amplifiers which are suitably biased to begin operation sequentially for increasing power requirements. Such a power amplifier is described in copending application Ser. No. 10/059,866, supra.

[0005] Conventional practice is to individually package each transistor amplifier in a housing, and then connect the packaged transistor amplifiers through impedance matching networks and signal splitters to a common input. However, the use of individual chip packages increases manufacturing costs and increases the total package footprint on a supporting substrate. Further, the mounting of several packages necessarily increases transistor spacing and signal phase differences between the transistors.

[0006] In accordance with the invention, a plurality of individual transistor amplifier chips are mounted within a single package with each chip having its own input and output leads. The chips can have unequal peripheries and gate widths, as often employed in a Doherty amplifier, and each chip can be pre-matched within the package for its input, output, and bias leads. The prematched transistor dice can then be used in high-efficiency amplifier designs, such as for carrier and peak amplifiers in a Doherty configuration.

[0007] The invention provides manufacturing efficiency and reduces the overall packaging footprint. Further, the transistor dice are in close proximity thereby minimizing phase differences in signals in the several transistors. For a Doherty application, the package must have twice the number of leads as there are chips in the package. This allows each transistor to be individually pre-matched within the package and individually biased.

[0008] The invention and objects and features thereof would be more readily apparent from the following detailed description and dependent claims when taken with the drawings.

[0009] FIG. 1 is a functional block diagram of an RF power amplifier for amplifying an RF signal over a broad range of power and employing a plurality of individually packaged power amplifiers as disclosed in copending application Ser. No. 10/059,866.

[0010] FIG. 2 is a plan view of an equivalent power amplifier to the amplifier of FIG. 1 in accordance with an embodiment of the invention.

[0011] FIG. 3 is a functional block diagram of the power amplifier of FIG. 2 connected as a four-way Doherty amplifier.

[0012] FIG. 1 is a functional block diagram of a power amplifier described in copending application Ser. No. 10/059,866, supra, which employs a plurality of individually housed power amplifier chips including a carrier amplifier 20 and three peak amplifiers 21, 22, 23, with the peak amplifiers connected through 90° transformers 24, 25, 26, to an output load 28. A 90° transformer 30 connects a four-way splitter 32 to carrier amplifier 20. By setting the DC bias on each of the peak amplifiers to appropriate values, the peak amplifiers allow a Doherty action to be extended. For each peak amplifier that is added above the first, there will be a corresponding increase of 6 dB in the power range over which the peak efficiency will be maintained. The four-way amplifier extends the range of efficient power to a theoretical value of 18 dB. Such extension is very important in digital communication systems using modulation schemes where the peak to average power ratios can be as high as 13 dB. A 120 watt peak amplifier can be provided by a four-way Doherty arrangement with each path (carrier and three peak amplifiers) utilizing 30 watt transistors.

[0013] The individual power amplifiers need not be of the same size and the chips can have unequal peripheries or gate widths. However, each power amplifier must be impedance matched to the input and appropriately biased so that sequential operation of the amplifiers is realized for a broad range of power operation.

[0014] FIG. 2 is a plan view of a package in accordance with the present invention in which the plurality of power amplifier chips 20-23 are mounted with housing 36. Each of the chips has its own input lead (RF input 1-RF input 4) and output lead (RF output 1-RF output 4). Further, each of the transistor chips 20-23 has its own impedance matching shown generally at 38 for the input, and shown generally at 40 for the output, and individually biased both for the gate and drain for a FET (base and collector for a bipolar device). Thus, for a Doherty arrangement the individual transistors can be matched differently and optimally as carrier and peaking amplifiers respectively.

[0015] FIG. 3 illustrates the four-transistor package 36 of FIG. 2 in a four-way Doherty amplifier. An RF input signal is applied through two-way splitters 50, 52, 54 to develop four input signals which are then applied through impedance matching circuitry 56 to the RF inputs of package 36. The outputs of the packaged amplifier 36 are applied through impedance matching circuitry shown generally at 58, and then summed as the RF output at 60.

[0016] The use of a single housing for a multi-transistor chip amplifier with individual leads provided in the housing for each amplifier chip not only lowers manufacturing costs, but the close proximity of the chips minimizes phase differences between the transistors. Additionally, the single housing reduces the amplifier footprint on a supporting substrate. While a four-chip Doherty amplifier has been described, the invention is readily applicable to a Doherty amplifier having a carrier amplifier and a single peak amplifier. Further, the invention is applicable to multistage amplifier transistors. The invention can be implemented using a wide range of semiconductor technologies including silicon bipolar, GaAs, MESFET, InGaHBT, SiC MESFET, and GaN HEMT, over a wide range of power levels and frequencies.

[0017] Thus, while the invention has been described with reference to specific embodiments, the description is illustrative of the invention is not to be construed as limiting the invention. Various modification and applications may occur to those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims.