Abstract - It has been previously shown that the allowed values of minimum noise temperature T min and N=Roptgn (Lange noise parameter) for any transistor ...
On Noise Properties of Transistors and Amplifiers A Critical Review Marian W. Pospieszalski National Radio Astronomy Observatory* C harlottesville, VA 2 2 903, USA
Abstract
-
It has been previously shown that the allowed
values of minimum noise temperature Tmin and N=Roptgn (Lange noise parameter) for any transistor have to satisfy inequality 1:S4NTo/Tmin:S2. Furthermore, it has been shown that in the useful frequency range for all transistors 4NTo/Tmin"'2. Experimental confirmations have been published for III-V FETs, HEMTs, HBTs (in several different technologies including GaN HEMTs), and CMOS devices. This paper examines the consequences of this fact for widely held and widely published assumptions in the treatment of noise in transistors and amplifiers, amongst those CMOS
"gate
induced
noise"
concept
and
CMOS
"noise
cancelling" amplifiers. It is shown that some long held concepts need
to
be
reexamined.
-
The
discussion
is
illustrated
with
experimental data.
Index Terms
Bipolar transistors; CMOS; FET; HEMT;
HBT; noise; noise measurement; low noise amplifiers
I.
INTRODUCTION
For a commonly used circuit representation of noisy linear two ports shown in Fig. 1, the minimum noise temperature Tmin can be expressed as [1], [2]:
(�
T 2 T N Re p R n g n min = o { +
�'
(1)
In this equation only Re(p) may assume negative values. C onsequently, if Re(p)::o-O, the following inequality must hold [1], [2]:
1�
4NlQ -�2
(2)
Tmm The left hand side of the inequality is a fundamental property of any noisy two-port reflecting the observation that two noise sources may not be more than perfectly correlated p :s 1), while the right hand side is satisfied only by certain noisy two ports for which Re(p)::O-O. It is important to notice that each component of the sum of right side of equation (I) is invariant under any lossless transformation at the input or output of a noisy two port.
(I I
provided an alternative proof of this property, extended its validity to passive reciprocal two ports (a rather important observation), gave an example of GaN device noise parameters satisfying (2 ) and also presented an example of non-reciprocal network (based on an isolator noise model [4]), the noise parameters of which violate (2) as expected. Also in a very recent paper J. L. Dietrich [5] re-discovered some of the properties which were known for quite some time [I], [2], [5]. However his attempt to establish general network conditions under which the right hand side of inequality (2 ) holds fell short. One can easily provide counter-examples with amplifiers using isolators [3], [4], amplifiers having strong complex feedback [2], [3] or balanced amplifiers [7], [2 8] for which the right hand side of (2) can be easily violated. In Section II, several examples of measured and/or modeled noise properties of several different FETs (high dynamic range low noise E-HEMT, InP cryogenic HEMT and CMOS) are described to further support the claim made by the author in [I], [2] that for practical devices and single ended amplifiers 4NTo/Tmin;:::;2 within typical measurement errors (the author refused the temptation to rename this ratio as "0wp" [3], as "q" [6], or as "n"[24]). A critique of certain concepts quite prevalent in published literature in view of these well proven observations is presented in Section III. In that discussion, we shall refer to the simplest noise model of an intrinsic FET shown in Fig. 2 .
LINEAR NOISELESS TWO-PORT
To�290
It has been shown by the author in [1], [2] that indeed generally accepted noise equivalent circuits of transistors satisfy Re(p)::0-0 and therefore must satisfy (2). A number of examples of measured noise parameters of transistors realized in different technologies have been presented in [2] and it has been shown that in the useful frequency range for all microwave transistors 4NTo/Tmin;:::;2 . Recently L. Boglione [3]
*The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
K
k -Boltzmann constant
Fig. I. Typical circuit representation of a noisy two-port, k is Boltzmann's constant, and To is 290 K.
" 40
30
I_I �
s. Mea
I
Noise Resitance ATF54143
2
6 4 Frequency (GHz)
I
for 3V/40rrA
- ... M:xlel Tg=3751
