IEEE Circuits and Systems Magazine - Q1 2020 - 14

In addition, different researches have investigated the
ability to measure blood glucose level noninvasively using optoelectronics methods [6]-[9]. Furthermore, Near
Infrared Spectroscopy (NIRS) is a state of the art technique that uses optoelectronics in which multiple near
infrared wavelengths are employed to measure different
brain blood chromophores like hemoglobin, oxy-hemoglobin and cytochrome c-oxidaze [10]-[14]. A block diagram
describing the building construction of an NIRS system
is shown in Fig. 3. NIRS has many current and future applications like brain function mapping [15], [16], epilepsy
seizure prediction [17], lung efficiency assessment [18],
and preventing hypoxia in open heart surgeries [19], [20].
Those mentioned optoelectronic devices in Fig. 1, 2 and 3
are very similar in their circuit architecture; they transmit
an optical signal to the human tissues and detect the reflected signal with a photodiode (PD).
In all of the previously mentioned biomedical devices, a PD converts the optical power into an electrical
photocurrent which is fed to a transimpedance amplifier
(TIA) for amplification and conversion to an output voltage. Two stages, a post amplifier and an output buffer,
are usually included in all of the mentioned previously
biomedical devices.

Optical
Fiber

There are many TIA topologies presented in the literatures. Each is designed for a certain biomedical application. Consequently, the main challenge facing every optoelectronic circuit designer is how to choose a suitable
TIA topology for the intended biomedical application regarding many aspects such as the transimpedance gain,
BW, input referred noise current, power consumption,
and dynamic range. Some of those aspects may be in a
direct trade-off with each other making the choice even
more challenging. Accordingly, this paper presents an
analysis, simulation, and comparison of eight different
state of the art TIA topologies helping the designer to
find the appropriate TIA that meets their requirements.
The investigated TIAs topologies in this study, including overall analysis, simulation, and comparisons, are
the common source TIA (CS-TIA) [21]-[24], the inverter based TIA (Inv-TIA) [25]-[28], the inverter cascode
based TIA (InvCas-TIA) [29], the regulated inverter cascode (RIC-TIA) [30], [31], the current reuse TIA (CR-TIA)
[32], [33], the current reuse with regulated cascode TIA
(CR-RGC-TIA) [34], the common gate TIA (CG-TIA) [35],
and the regulated cascode TIA (RGC-TIA) [22], [36]-[38].
All of the investigated topologies are simulated using
130 nm standard CMOS technology with the same 1.2 V

Transceivers Multi-Channels
Post
Amplifier
and
O/P Buffer

TIA

ADC

AGC
TIA + Power
Detector

Monitor
PD
Optode
Laser
Driver

DAC

PC
Microcontroller Unit

Figure 3. A block diagram of an NIRS device.
14

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