IEEE Solid-States Circuits Magazine - Fall 2023 - 22

TABLE 3. COMPARISON BETWEEN ACADEMIC RESEARCH AND COMMERCIAL SOLUTIONS.
SYMPOSIUM
ON VLSI
CIRCUITS
2021 [18]
Area (mm2)
Rec. channel
Total area/Ch (mm2)
Tran. type4
IRN (nVrms)
20
1024
0.020
Wireless
8.98
ICCSS
2023 [23]
4
128
0.031
≈20.9
JSSC 2023 [17]
0.64
128
0.005
11.9 (LFPs), 7.71
(spikes)
RHS21161
23.42
16
1.464
Wired connection
2.4
RZ5D
BIOAMP2
N/A
32
N/A
≈85
1Developed by Intan Technologies. Technical specifications: https://intantech.com/files/Intan_RHS2116_datasheet.pdf.
2Developed by Tucker-Davis Technologies. Technical specifications: https://www.tdt.com/files/manuals/hardware/RZ5D.pdf.
3Developed by Brain Products GmbH. Technical specifications: https://www.brainproducts.com/solutions/actichamp.
4Tran. type: transceiver type.
5Calculated by other data provided.
cable used for data/command communication.
The limited space may
cause the animal subject to feel isolated
[24], resulting in motion artifacts
and errors in the results of the
experiments [25]. In addition, the use
of the wired connection introduces a
high risk of potential infection [26].
Customized wireless neural interfaces
have been reported in the literature
[2], [3], [27], a common block
diagram of which is shown in Figure 1.
Such designs allow neuroscientists
to study the principle of neural activities
when the small animals move
around and interact with other freely
moving subjects. At the expense of a
little noise performance, they reduce
the total chip area per channel and
transmit data wirelessly, making the
whole interface smaller and more
convenient to use. However, the increase
of the total electrode channels
placed a challenge on the total
silicon area,
the wireless throughput,
and the battery life.
Area-Efficient AFE
The AFE is directly connected to the
electrode for signal amplification and
digitization. The total silicon area and
the power consumption of the front
end are proportional to the channel
number. The AFE is a key module
that determines the performance of
the noise, linearity, input range, and
impedance of the neural interface.
As shown in Figure 2, existing popular
solutions can be classified into
two types:
1) the capacitively coupled chopper
amplifier (CCIA) + ADC solution
2) the so-called ADC-direct digitizing
structure.
Compared with traditional instruCH1
CH2
AFE
AFE
Neural
Signal
Processing
Units
AFE
CHN
Power Management
Wireless
Tx/Rx
FIGURE 1: A block diagram of a wireless compact neural interface for freely moving
animal subjects.
22
FALL 2023
IEEE SOLID-STATE CIRCUITS MAGAZINE
mentation amplifiers, the CCIA features
higher rail-to-rail input range
and higher power efficiency [28], [29],
[30], [31]. Chopping technology can effectively
reduce the 1/f noise. Various
techniques have been used to improve
the performance of the CCIA framework.
The ripple attenuation loop is
used to reduce the residual ripple after
chopping [29]. The positive feedback
loop can be added to increase
the input impedance. For biological
applications with a large electrode dc
offset, by adding the dc servo loop,
the output signal is fed back to a virtual
ground to eliminate the dc component
[30]. However, the area of the
CCIA framework is relatively large due
to the use of big capacitors to reduce
ACTICHAMP3
N/A
160
N/A
2.0

https://intantech.com/files/Intan_RHS2116_datasheet.pdf https://www.tdt.com/files/manuals/hardware/RZ5D.pdf https://www.brainproducts.com/solutions/actichamp

IEEE Solid-States Circuits Magazine - Fall 2023

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