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32 Channel Analog Headstage
Version 2
Design Review Suggestions for Version 1
-
-
The Headstage should be a drop in replacement for the Plexon Headstage.
preferably a one-board solution rather than adding a second voltage regulator
board.
Adjust the capacitor pad sizes so that it is easier to replace capacitors with 0 Ohm
resistors to get low frequency signals
Placement of decoupling capacitors could be improved.
Reduced the power plane by 10-20 mils so that it doesn’t get shorted out on the
edges.
Wider pads for the input and output pins
Careful about the side entries
Needs thickness estimate
Reduce number of vias and see if it could be hand routed better.
Changes made from the first version of Headstage
2.5V shunt voltage regulator is added to the board to make sure power supply does not
exceed max supply range for amplifier.
Improved placement of decoupling capacitors: four discrete 0.47uF decoupling capacitors
are placed on the four corners of the board (two on front side and two on back side of the
board).
Changed footprint for capacitor array to match the resistor array making it easier to
replace the 0.1uF array with a resistor array (possibly a 0 resistor array).
Increased the size of the Omnetics connectors to improve ability to solder pins onto board
New routing to reduce number of vias, improving the function of power planes as well as
reducing cost of board.
32 Channel Analog Headstage
The Analog Headstage uses Linear® LTC6079 CMOS operational amplifiers and noninverting configuration architecture to provide amplification. It provides 10x gain for 34
channels, 32 of which are used for recording for high impedance electrodes (Channels 132). The remaining two channels are used to generate reference signals, which will be
used differentially to subtract common mode noise at the Preamplifier stage.
OMNETICS
38 PIN MALE
NANO
CONNECTOR
Top View
1.66in.
OMNETICS
38 PIN MALE
NANO
CONNECTOR
OMNETICS
36 PIN FEMALE NANO
CONNECTOR
0.620in.
OMNETICS
36 PIN FEMALE NANO
CONNECTOR
1.300in.
Bottom View
Figure 1: Headstage Board Dimensions
Length: 1.66 in
Width: 0.62 in
Thickness: 0.10 in
I. System Overview
The 32 channel Analog Headstage is designed to interface with a version of the
Plexon Preamplifier (PBX/32sp).
Electrodes
Analog
Headstage
Plexon Preamplifier
Figure 2: System Overview
Headstage Electrical Specifications
II. Schematic
The circuit configuration shown below is used for all 32 channels as well as the 2
additional reference channels.
Figure 3: Non-inverting configuration used to set gain
Gain
Bandwidth
10
530Hz – 75KHz
III. Power Supply
Power
Supply
Headstage
Plexon Preamplifier
600 Ω
100Ω
3 mA
DC
1uF
2.5V
15uA-15mA
1uF
Load
DC
600 Ω
100Ω
3 mA
Figure 4: Power supply connections
The Headstage uses the same power supply as the Plexon preamplifier. However,
a 100 resistor lies in series before the power supply input to the Headstage.
The Headstage has an on board shunt voltage reference: a 600 resistor and a 2.5V high
precision shunt mode voltage reference (Analog Device: ADR525B, which has an
operating current range of 50uA-15mA).
The current consumption of the Headstage and the power dissipation across the
combined series 700 resistor is given below for two power supply cases.
Power Supply
Current drawn from supply
 6V
 5V
5 mA
3.57 mA
Power dissipated across
resistors (100 & 600)
17.5 mW
8.92 mW
a. Decoupling Capacitor:
A total of 1.04uF ceramic decoupling capacitors exist between positive
power supply and ground as well as negative power supply and ground.
Noise
The input noise of the Headstage calculated over the bandwidth range of 530 Hz75KHz, and is 4.91 uVrms. The input noise that the Headstage introduces into the system
is calculated over the bandwidth of interest (530Hz-8KHz, bandwidth of the preamplifier
stage) is 1.55 uVrms
Output Impedance
The output impedance for each channel of the Headstage vs. frequency is given
by the Av =10 curve shown below.
Figure 5: Output impedance for Linear® LTC6079 CMOS Op amp (Linear Data Sheet).
Capacitive Load
The Headstage can drive capacitive load up to 200 pF. A small series resistance
between the output and the load further increases the amount of capacitance the amplifier
can drive.
Connectors
Input Connector: Omnetics A8649-001
Mating Input Connector: Omnetics A8648-001
(This is the input connector used on the Plexon Headstage HST/32o25-36P)
Pinout Information
Pin
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Function
Ref #2
Channel 17
Channel 18
Channel 19
Channel 20
Channel 21
Channel 22
Channel 23
Channel 24
Channel 25
Channel 26
Channel 27
Channel 28
Channel 29
Channel 30
Channel 31
Channel 32
GND
Pin
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
Function
GND
Channel 1
Channel 2
Channel 3
Channel 4
Channel 5
Channel 6
Channel 7
Channel 8
Channel 9
Channel 10
Channel 11
Channel 12
Channel 13
Channel 14
Channel 15
Channel 16
Ref #1
Output Connector: Omnetics A8237-001
Pinout Information
Pin
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Function
V+
GND
Channel 1
Channel 2
Channel 3
Channel 4
Channel 5
Channel 6
Channel 7
Channel 8
Channel 9
Channel 10
Channel 11
Channel 12
Channel 13
Channel 14
Channel 15
Channel 16
Ref #1
V-
Pin
Function
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
Ref #2
Channel 17
Channel 18
Channel 19
Channel 20
Channel 21
Channel 22
Channel 23
Channel 24
Channel 25
Channel 26
Channel 27
Channel 28
Channel 29
Channel 30
Channel 31
Channel 32
GND