IEEE Circuits and Systems Magazine - Q3 2022 - 29

C4 1p
C2
VREF
10p
C1
VREC
10p
C3
1p
R1
Figure 6. The single-channel preamplifier.
to the internal chopper, notch filter and zero-drift module.
The voltage gain of the CCIA is given by
A =
V
()
14
1
+
ET
ET
CC C
CC
.
C
C
4
1
(1)
where CET is the equivalent capacitance of the electrode
and C4 is the feedback capacitance. The lower cutoff frequency
of the CCIA is [22], [25]
fL =
2 RC
1
r 24
(2)
where R2 is the resistance of the pseudo-resistor (which
is implemented with two p-channel MOSFETs, i.e., BSS84,
ON Semiconductor). The CCIA are cascaded by a non-inverting
amplifier and a 2nd-order low pass filter (LPF, to
filter out signals above 200 Hz). A coupling capacitor C5
is inserted between amplification stages to further compress
the EDO and the DC offset. When both the EDO
and the PLI are effectively attenuated, the required resolution
of the subsequent ADC can be low (i.e., around
11-12 bits), which makes the use of the internal ADCs of
the MCU possible.
The measured gain and the integrated input-referred
noise (IRN) of the preamplifier (in the frequency band
of interest from 1Hz to 200Hz) are 45.8dB and 4.9 μVrms,
respectively, as shown in Fig. 7 and Fig. 8. Table I shows
performance of the recording front-end compared with
commercial biopotential ICs (such as AD8233 [26] and
ADS1299 [27]).
VI. Thresholding Epileptic Seizure Detector (TESD)
The EEG signals in the ictal period is different from
the EEG signals in the inter-ictal (seizure-free) period
(Fig. 9), which is characterized by a series of spike
wave discharges (SWD's) with relatively large amplitude
(Fig. 10). Therefore, the thresholds of magnitude
in the time domain or the power spectrum density
in the frequency domain can be used for the TESD.
THIRD QUARTER 2022
20
10
10-2
10-1
100
101
102
Frequency (Hz)
Figure 7. Gain of the preamplifier.
103
104
Simulation
Measurement
50
40
30
R2
-
+
TLVx333
10u
C5
+
R3
10k
-
+
TLVx333
R5 200k
R4
200k
R6
50
C6
R7 Vout-EEG
++
4.7u C7 4.7u
50
10-5
Measurement
Simulation
10-6
10-7
10-8
10-9
100
101
Frequency (Hz)
Figure 8. IRN of the preamplifier.
IEEE CIRCUITS AND SYSTEMS MAGAZINE
29
102
4.9 µ Vrms
1-200 Hz
IRN (V/sqrt (Hz))
Gain (dB)

IEEE Circuits and Systems Magazine - Q3 2022

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