IEEE Solid-States Circuits Magazine - Fall 2023 - 21

EEG, local field potentials (LFPs),
and neural spikes are currently the
most important measurement signals
of neural interfaces. The common
frequency and amplitude ranges
[12] and the front-end requirements
of the above three electrophysiological
signals are shown in Table 1.
EEG signals are small in amplitude
(on the order of 10 nV) and low in frequency
(less than 100 Hz). Due to the
low amplitude, the acquisition equipment
needs to have extremely high
noise suppression capability, and
high precision is required for the ADC.
There are already mature commercial
devices for collecting EEG signals;
LFP signals are also low in frequency
but have high signal amplitude. Compared
with EEG signals, the measurement
of this signal requires relatively
low noise suppression. Cutting-edge
neural interfaces for measuring LFP
signals are presented in [13], [14], [15],
and [16]. The neural spike signal features
high frequency and amplitude
at the same time, which requires the
neural interfaces to enable a high
sampling rate and bandwidth.
Considering the actual intrusive
acquisition conditions,
the corresponding
neural interface for LFPs
and neural spikes needs to have ultrasmall
power consumption and
volume. The parameters of six representative
neural interfaces are
TABLE 1. THE FRONT-END REQUIREMENTS OF EEG, LFPS, AND NEURAL SPIKES.
EEG1
Frequency (Hz)
Amplitude (nV)
IRN (nVrms)
CMRR (dB)
Bandwidth (Hz)
Channel number
0.1-100
1-10
≈1
>100
≈100
4, 8, 16, 32, 64, 128,...
1Refer to the datasheet of commercial products like RHS2116 (Intan Technologies), KS1092 (Kingsense), and ADS1299 (Texas Instruments). IRN: input
referred noise.
TABLE 2. STATE-OF-THE-ART WIRELESS COMPACT NEURAL INTERFACE DESIGNS.
ISSCC 2018
[21]
Process (nm)
Area (mm2)
Type
Application
Max stim. current (mA)
Stim. channel
Rec. channel
Rec. power/Ch (nW)
Rec. area/Ch (mm2)
AFE bandwidth (Hz)
IRN (nVrms)
CMRR (dB)
130
N/A
OStim./Rec.2
LFPs, spikes
35
4
10
11.2
N/A
0.1-7,000
3.2
N/A
JSSC 2020
[13]
130
1.14
EStim./Rec.2
LFPs, ECG
1.35
16
16
0.99
0.011
1-500
2.6
>78
SYMPOSIUM ON
VLSI CIRCUITS
2021 [18]
65
20
EStim./Rec.
LFP, spikes
0.6
1024
1024
2.72
0.0062
5-10,000
8.98
92.6
1Neural implant IC/ body-coupled communication (BCC) RX IC.
2OStim.: optical stimulation; Rec.: recording; EStim.: electrical stimulation.
3Calculated by other data provided.
IEEE SOLID-STATE CIRCUITS MAGAZINE
FALL 2023
21
JSSC 2022
[22]
110/1801
4/0.31
Rec.
Spikes
/
/
4
8.6
0.04
10,000
6.6
N/A
ISSCC 2023
[23]
65
4
Rec.
Spikes
/
/
128
9.87
0.02
10,000
≈20.93
N/A
JSSC 2023 [17]
22
0.64
Rec.
LFP, spikes
/
/
128
6.02
0.0045
0.1-10,000
11.9 (LFPs), 7.71 (spikes)
N/A
LFPS [13], [14], [15], [16]
0.1-100
100-1,000
≈2
>80
400-800
listed in Table 2. Typically, the recording
power per channel is about
10 μW, and area per channel is usually
around 0.01 mm2.
Since a few commercial devices
are widely used in neuroscience research
to record electrophysiological
signals, a comparison is made
between those commercial implants
or chips with the results of academic
research, which is shown in Table 3.
The first three columns are published
works on wireless neural interface designs,
and the others are commercial
devices or chips.
Commercially available solutions
typically keep laboratory animals
confined to a small area due to the
NEURAL SPIKES [17], [18], [19], [20]
100-1,000
100-1,000
>10
/
10,000
IEEE Solid-States Circuits Magazine - Fall 2023

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