IEEE Circuits and Systems Magazine - Q1 2020 - 27

Table XI.
A comparison between the reviewed TIA topologies at CPD = 2 pF and 100 MHz BW while targeting minimum noise.
Topology

Gain
(dBΩ)

BW
(MHz)

Total Integrated
Input Noise nA rms

Power
μW

I Ovl
p -p
μA p -p

DR
(dB)

FoM1

FoM2

CS-TIA

72.6

100

570

99.1

69.5

45.3

4492.8

Inv-TIA

78.9

100

25.3

570

69.8

122.2

9531

InvCas-TIA

95.6

100

22.6

570

935.5

3742

RIC-TIA

96.3

100

24.6

570

1.1

931.6

1024.7

CR-TIA

80.2

100

35.5

570

0.93

28.4

101.1

94.1

CR-RGC-TIA

83.1

100

570

0.32

17.4

116.6

37.3

CG-TIA

100

45.8

100

61.6

173.8

9561.5

RGC-TIA

85.5

100

41.6

100

54.1

905.6

19017.6

FIRST QUARTER 2020

it is clear that the noise performances of the CG-TIA and
the RGC-TIA are the worst among the studied topologies.
Thus, it is advisable to avoid using CG-TIA and RGC-TIA
if the input referred noise and the sensitivity are of the
highest concern.
D. Case 4: CPD = 2 pF, 100 MHz BW, Minimum Power
The frequency response and the input referred noise current spectral density of the reviewed TIAs are shown in
Figs. 18 and 19 respectively. Also, a summary of the obtained simulation results for the minimum power case and
100 MHz BW is listed in table XII. Once again, higher open
loop gain topologies achieves better performance regarding the first four topologies. InvCas-TIA achieves lower
power consumption and higher GBW at the same input

90
Transimpedance Gain (dBΩ)

GBW because of the former superior effective transconductance. On the other hand, the InvCas-TIA achieves
higher dynamic range and slightly lower input referred
noise at the same power consumption. Furthermore,
the Inv-TIA has a better GBW and noise performance
compared to the CS-TIA at the same consumed power.
Both the CS-TIA and the Inv-TIA attain the highest DR
due to their high I Ovl
p-p.
Comparing the CR-TIA with the CR-RGC-TIA, the latter
achieves higher transimpedance gain at the same power
consumption. However, this comes at the expense of a
higher input noise and lower DR. This explains why the
design reported in [34] needed an automatic gain control
to obtain a reasonable dynamic range for its intended
biomedical application. In addition, CR-TIA and CR-RGCTIA outperforms CS-TIA in terms of GBW and FoM 1 at
the same consumed power. Also, CS-TIA has the superiority in term of FoM 2, linearity, and DR at the same
power consumption.
At higher BW and relatively higher biasing current,
the results of both CG-TIA and RGC-TIA become reasonable. Regarding the RGC-TIA, the regulation of the cascode transistor greatly boosts the effective transconductance resulting in a noticeably higher GBW compared to
the CG-TIA. Consequently, the RGC-TIA outperforms the
CG-TIA in all aspects except for the DR because of its
higher transimpedance gain. One important observation
is that the RGC-TIA achieves better noise performance at
the same power consumption of the CG-TIA despite the
extra components of the regulating amplifier. This is because the RGC-TIA needs less biasing current to attain the
same effective transconductance for the cascode transistor; since g mn is multiplied by ( ; A rg ; + 1) as described by
equation (33). Consequently, lower biasing current (lower
g mnB) means lower noise contribution from the dominant
noise source (the biasing current source) which is directly proportional to g mnB, see equation (37). Furthermore,

85
80
75
70
65
60
100

10 K 100 K 1 M 10 M 100 M 1,000 M
Frequency (Hz)
CS-TIA
Inv-TIA
InvCas-TIA
RIC-TIA

CG-TIA
CR-TIA
CR-RGC-TIA
RGC-TIA

Figure 18. Frequency response of the reviewed TIAs while
targeting min power and 100 MHz BW.

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