Biomedical Engineering Reference
In-Depth Information
band-limited signal can be expressed as a lowpass filtered version of an appropriately weighted sum
of delayed impulse functions, which is expressed in equation (
1
). So the signal recovery problem is
how to calculate the appropriate weights. We can define the timing of pulses:
T
= [
t
1
,
t
2
, …,
t
k
,
t
k + 1
, …].
Let
(
t
) =
v
in
A
in
-
V
ref - supply
+
V
mid
. Substituting equation (
7.2
) into equation (
7.1
), we obtain
t
t
t
i
+
1
i
+
1
i
+
1
∫
∑
∑
∫
∫
θ
=
y
(
t
)
d
t
=
w
h
(
t
−
t
)
d
t
=
w
w
h
(
t
−
t
)
d
t
(7.3)
j
j
j
j
j
j
j
t
t
t
i
i
i
t
i
+
1
∫
(7.4)
c
=
h
(
t
−
t
)
d
t
ij
j
t
i
which can be rewritten in matrix notation as
CW
= θ. Unfortunately,
C
is usually ill-conditioned,
necessitating the use of a SVD-based pseudoinverse to calculate the weight vector
w
. We have
extended the reconstruction algorithm to work for a biphasic pulse train with positive and negative
pulse indicating when a positive or negative threshold is surpassed [
59
].
7.5.2 wireless
A wireless interface for the FWIRE microsystem is currently being developed to facilitate in vivo
neural recording in behaving animals. As shown in Figure
7.17
, the system includes a power recov-
ery, regulation, and battery management module; an ASK clock and data recovery (CDR) circuit to
download external system commands; a transmitter and signal processing circuits to upload neural
data from the various recording channels; and a small controller with register bank to oversee sys-
tem functionality, decode/encode data packets, and store on-chip settings. All components are fully
integrated with the exception of the power/downlink coil, the uplink antenna, and the battery.
FIgURE 7.17:
Wireless interface system block diagram.
