Distributed Power Amplifier with Multi-Section Transformer
Original Publication Date: 2009-Mar-09
Included in the Prior Art Database: 2009-Mar-09
Narendra Kumar Aridas: INVENTOR [+2]
Distributed Amplifier (DA) is a creative methodology to improve gain bandwidth product . A design proposal to achieve high gain and efficiency DA with low supply DC voltage is given.
By Narendra Kumar Aridas and Pragash Sangaran
Advance Technology Group (ATG)
Distributed Amplifier (DA) is a creative methodology to improve gain‑bandwidth product . A design proposal to achieve high gain and efficiency DA with low supply DC voltage is given.
Suitable device technology such as pHEMT allows low supply DC voltage which is well-suited for 2-way communication radios applications. Due to higher input parasitic capacitance (Cgs) of pHEMT device, series capacitively coupled is recommended at gate line, but, reduces gain and efficiency of DA.
Zhao et al  has showed DA applying pHEMT device (with 3.2V supply) and transforming from 3.3 W to 50 W with LTCC transformer where the authors have demonstrated 800 MHz-2.1 GHz for 1.2 W. US 6,614,307 has shown hybrid DA with transformer balun . The transformer demonstrated in DA has moderate bandwidth in principle and introduces losses. Recent state-of-art of the broadband transformer  showed improvement for wide band frequency range.
This invention is mainly to achieve high gain and efficiency for broadband frequency with low supply DC voltage. Refer to Figure 1 for the invention topology. Two non-identical transistors are cascaded , where the lower and upper FETs are featured by high gate periphery ratio. An adjustable inter-stage matching cascaded network is proposed to achieve optimum broadband matching between two non-identical transistors, in the entire bandwidth. The basic design principle of DA, based on forming two artificial transmission lines, still applies in this design, i.e. phase alignment between input and output lines, as well as equalization of the RF drive signal at the input of each device.
Broadband transformer based on asymmetric parallel coupled line is proposed with DA . The transformer is having an optimum wave-length. More section of the transformer is significantly improved wideband frequency range with minimum return loss (more number of zero reflections) as shown in Figure 1. However, the electrical length can be reducing with compensation of number of section. Implementation in homogenous medium is possible to reduce size constraints.
The invention is verified (in simulation) with 2-stage non-identical
pHEMT devices; lower stage FET (ATF541) is having (Cgs=2.3 pF and Cds=0.8 pF, respectively) and upper stage FET (ATF511) is having (Cgs=10.1 pF and Cds=2.8 pF, respectively). The gate-width of the FETs is 800um and 6400um, respectively. The lower and upper stage FETs are fed with 3 V and 4.5 V drain supply voltage, respectively. The input of lower stage FET is connected along gate line to achieve wide BW range (since Cgs is lower). This avoid a big voltage drop with series capacitively coupled netwo...