IEEE Solid-States Circuits Magazine - Spring 2021 - 32

assembled amplifier appears in Figure
9(e). As demonstrated in Figure 9(f),
the measured noise averages just
3.2 K from 4 to 8 GHz. While this is
a significant step toward demonstrating
that SiGe HBTs can provide
competitive cryogenic performance
in this frequency range, it was just
a first step in tweaking a commercial
process for improved cryogenic
noise performance, and, with additional
research, it will likely be feasible
to realize SiGe HBTs with even
lower noise.
Significant progress has also been
made in translating these discrete
amplifier results into IC form. A
4-8-GHz LNA consuming 058 Wn
while achieving a noise temperature
and input(output) return loss at
T 18K
a =
4 K (.006dB) when operated at
T ..16 5K Ongoing work is focused
NF1
a =
on reducing both the power and noise
of integrated SiGe cryogenic LNAs.
Integrated low-power cryogenic
SiGe LNAs are also being developed
for systems applications. For example,
the 0.1-3-GHz cryogenic LNA IC
presented in Figure 10 was developed
for integration in a 1.9-THz focal plane
array based upon HEB mixer technology.
A major challenge addressed in
this design is extending the bandwidth
to the lowest frequencies
possible, which is important when
designing an HEB mixer-based system
since the upper frequency of an
HEB mixer is limited to 3GHz.
by the
of approximately 8 K and
12(15) dB, respectively, was implemented
in Global Foundries BiCMOS8HP
technology [70]. Moreover,
it was shown experimentally that the
power of this device could be reduced
to about 00
4Wn with little impact
on the gain and noise performance.
Additional SiGe low-power cryogenic
LNA ICs that have been demonstrated
include a 0.9-mW, 22-GHz LNA with
a noise temperature below 35 K
(.05NF dB)
1
at T 15K [73] and
a =
a 3-mW 2-4-GHz LNA with 28 dB of
gain and a noise temperature below
mixer's thermal time constant, making
it extremely important to capture
as much of the available bandwidth as
possible. While consuming less than
1 mW of dc power, this amplifier
offers input and output return losses
better than 7 and 15 dB over the entire
operating band, respectively. Moreover,
at a physical temperature of 15 K,
the noise temperature averages 4.6 K
(.007dB)
NF=
over the passband.
Referring to Figure 10(c), similar performance
is achievable even when
the power is reduced by as much as
20%. This project is ongoing, and further
work is required to integrate the
amplifier with an HEB mixer array.
Recently, we have also demonstrated
a low-power reconfigurable 3-6-GHz
cryogenic BiCMOS LNA (Figure 11)
implemented in a 180-nm Tower Semiconductor
SBC18S5 BiCMOS process
[75]. The circuit consists of a wideband
input stage that provides a broadband
noise match followed by a pair of buffered
reconfigurable second-order systems.
Each of the base-bias voltages
is generated using an on-chip resistive
digital-analog converter (DAC)
that provides a resolution of
250Vn ,
alleviating the need for external highprecision
supplies.
These DACs consume less than
1Wn each, making them ideal for
integration into low-power cryogenic
LNAs. The frequency and bandwidth
of the IC are controlled via the pair
of reconfigurable tank circuits,
details of which are described in
[75]. When configured for wideband
operation [Figure 11(c)], the amplifier
achieves a gain of greater than 35 dB
and an average noise temperature of
4.3 K while dissipating just 1.8 mW.
Remarkably, the frequency response
can be changed without affecting the
noise performance. For instance, the
responses illustrated in Figure 11(d)
and (e) demonstrate a nearly 9:1 range
in bandwidth with little change to the
in-band noise performance. Similar
tuning is also possible with respect
VCC1
VCC2
0.5
10
In
VBB1
VBB2
(a)
Out
1
2
3
4
5
6
7
8
9
0 0.1
(b)
0.2
0.3
0.4
0.5 GHz
1 GHz
2 GHz
3 GHz
0.7 0.9
Total Power (mW)
1.1 1.3
1.5
1.7
0.5
Input Stage Collector-Emitter Voltage (V)
(c)
FIGURE 10: A low-power SiGe cryogenic LNA for HEB readout [74]. (a) The schematic diagram. (b) The amplifier die micrograph. The IC measures
4.5 mm × 1.4 mm. (c) The measured noise as a function of the collector-emitter voltage of the input stage transistor. The actual applied
supply voltage (Vcc1) was 170 mV higher due to resistive voltage drops.
32
SPRING 2021
IEEE SOLID-STATE CIRCUITS MAGAZINE
0.6
Noise (K)

IEEE Solid-States Circuits Magazine - Spring 2021

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