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MMIC Amplifiers: Current
Limitations below 2 GHz
The noise figure and linearity of
low noise amplifiers are critical
factors in maximizing sensitivity
and dynamic range in RF receiver
design. The amplifier noise figure
determines the weakest signal the
amplifier can discern, and the IP3
determines the degree to which
intermodulation products from
nearby signals interfere with the
desired signal. The lower the noise
figure and the higher the IP3 of the
amplifier at the receiver input, the
greater the sensitivity and Spurious
Free Dynamic Range (SFDR) of the
receiver.
Today, the market availability of
single-function MMIC LNAs with
coverage to roughly 40 MHz and
above. External matching networks
and feedback can be applied
to extend coverage down to 1
MHz, but this has been known to
degrade noise figure performance.
While PHEMT designs generally
provide outstanding noise figure
performance and very high IP3 for
popular wireless applications from
Wi-Fi (2.4 GHz) through WLAN (5.6
GHz), options for applications below
2 GHz almost invariably sacrifice
noise figure performance, leaving
the densely utilized HF, VHF and
UHF application bands from 3 to
2000 MHz underserved.
MMIC amplifiers currently on the
market within the HF/VHF/UHF
region are limited by noise figure
performance no less than 2 dB.
MMIC Amplifiers Stretch the Boundaries of Dynamic
Range in VHF/UHF Communications
Radha Setty, Guangyue He and Brandon Kaplan, Mini-Circuits
high dynamic range is concentrated
around the ISM frequency bands
between 2 GHz and 6 GHz. These
amplifiers are predominantly PHEMT
or HBT designs on GaAs, and both
come with inherent advantages and
drawbacks. HBT designs are capable
of achieving very wide bandwidths
and excellent power density with
saturated output power up to 1W
through about 6 GHz. However HBT
designs generally aren’t conducive to
low noise, typically achieving about
3 dB noise figure at best, making
them unsuitable for receivers where
higher sensitivity is required.
PHEMT designs are capable of
realizing noise figures below 1 dB
and IP3 above 40 dB but existing
approaches are limited in frequency
36 l New-Tech Magazine Europe