Publicated in The International Society for Optical Engineering’s – Microtechnologies for the New Millennium Design (VLSI Circuits and Systems Conference), Gran Canaria, España, 2007

1. A 3-10 GHz Ultrawideband SiGe LNA with Wideband LC
Matching Network
J. del Pino, S. L. Khemchandani, H. García, R. Pulido, A. Goñi, A. Hernández
Publicated in The International Society for Optical Engineering’s –
Microtechnologies for the New Millennium Design
(VLSI Circuits and Systems Conference),
Gran Canaria, España, 2007
Abstract
A fully-integrated SiGe wide band amplifier implemented in a standard low cost 0.35 µm process up to 12 dB of gain and a bandwidth of 3-10 GHz
is presented. This circuit is divided in 3 stages. The first one is the input matching where the use of an inductively degenerated amplifier is
expanded by embedding the input network of the amplifying device in a multisection reactive network so that the overall input reactance is
resonated over a wider bandwidth. The second stage is a cascode transistor to obtain a great power gain and a high isolation between input and
output ports. In addition, by adjusting the area and the multiplicity of these transistors, we can reduce the noise figure of the circuit. Finally at
the output a new technique is used to increase the bandwidth. This technique is based in the replacement of the load resistor by a shunt-peaking
resistor composed by an inductor and a resistor. The addition of an inductance gives an output impedance that remains roughly constant over a
broader frequency range.
SiGe LNA Measurements & Simulations
Fig.1 LNA Schematic. Fig.2 LNA Layout.
• There are few examples of development of high-frequency wideband
amplifiers employing silicon transistors. Most of them are distributed
amplifiers which require high levels of power consumption, high area,
and they are not optimized for noise.
• Wide band impedance matching expands the use of an inductively
degenerated amplifier, by embedding the input network of the amplifying
device in a multisection reactive network so that the overall input
reactance is resonated over a wider 0
bandwidth.
• This work uses this methodology to extend the reactively matched LNAs
to wide bandwidths. It is shown that this approach satisfies the tough
system requirement of a UWB system with moderate power consumption. Fig.3 Measurements vs Simulations.
The proposed methodology makes extensive use of spiral inductors. The
problem here is that the overall amplifier gain should be flat across the
pass-band whiles the frequency response of integrated inductors is not.
Conclusions
Integrated Inductors
In this work we have reported the fundamental design aspects of
• Silicon is a low resistivity substrate and high quality integrated inductors wideband low-noise amplifiers with SiGe transistors and on chip
are difficult to obtain. inductors. A description of the LNA configuration was explained
• Inductors quality factor is limited by resistive losses in metal traces, emphasizing the influence of the design parameters in the circuit
induced currents in metal strips and substrate, and by metal to substrate performance. As an example a wide band amplifier with on-chip
capacitance. matching network spanning 3–10 GHz is presented. The circuit was
• The used technology has four metal levels. Three of them are similar and implemented in a standard low cost 0.35 µm process and provides a
the top level metal is thicker and with greater conductivity than the others. worst case maximum gain of 11.6 dB. The noise figure ranges from
Although the foundry offers a set of inductors, they are not designed for 3.5 to 7.5 in the band between 2 GHz and 8.5 GHz. The circuit core
our specific application. Particularly, the quality factor is not as high as we
draws 5.3 mA from a 3.3-V supply.
need (from 5 to 7), or is not centered at the required frequency.
• We have used Momentum©, from Agilent Technologies, a fast 2.5-
dimensional electromagnetic simulator to simulate spirals with different
geometry.
• An inductor library for the UWB band was designed. Acknowledgments
• With the designed inductors, we have achieved a high quality factor (from This work is partially supported by the Spanish Ministry of Science and
10 to 12). Technology (Ministerio de Ciencia y Tecnología, TEC2-005-06784-C02-02 and
FIT-330100-2005-268).
INSTITUTO UNIVERSITARIO DE MICROELECTRÓNICA APLICADA (IUMA)
UNIVERSIDAD DE LAS PALMAS DE GRAN CANARIA (ULPGC)