TDT RA4LI Application guide

Low Impedance Headstages
Hardware Reference
Updated 2021-09-15

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Low Impedance Headstages | 2

Table of Contents
Low Impedance Headstages
4RA4LI - Four Channel Headstage
4Impedance Checking with the Low-Impedance Headstage
5Headstage Voltage Range
5RA4LI Technical Specications
5RA16LI - 16 Channel Headstage
6Impedance Checking with the Low-Impedance Headstage
6Headstage Voltage Range
7RA16LI Technical Specications
8RA16LI-D - 16 Channel Headstage with Differential
9Headstage Voltage Range
9RA16LI-D Technical Specications
9Pinout Diagram
Table of Contents | 3

Low Impedance Headstages
RA4LI - Four Channel Headstage
The RA4LI headstage is designed for low impedance electrodes with input impedance between
< 1 kOhm and 20 kOhm. Electrode connectors are standard 1.5 mm safety connectors making
it easy to connect to standard needle and surface electrodes for recording evoked potentials
and EEG's. The headstage connects directly to the RA4PA Medusa preamplier's 25-pin
connector. A built-in impedance checker can be used to test each channel and the reference.
Additional 20x gain on the headstage improves signal-to-noise of low voltage signals.
Impedance Checking with the Low-Impedance Headstage
The Impedance checker on the RA4LI provides a simple check of the channel impedance
relative to ground. To check the impedance level, press the button next to the channel
indicator. The highest-level light indicates the maximum impedance between the channel and
the ground. If all impedance lights are illuminated it is likely that one of the channels is not
properly connected. The (-) impedance button checks the impedance between the reference
(black connector) and the ground (green connector).
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Headstage Voltage Range
When using a TDT preamplier the voltage input range of the preamplier (PZ5, Subject
Interface, RA16PA) is typically lower than the headstage and must be considered the effective
range of the system. Also keep in mind that the output range of the headstage varies
depending on the power supply provided by the preamplier. PZ5 and Subject Interface supply
± 2.5 V. PZ2 and RA16PA preampliers supply ± 1.5V. Third party preampliers may vary. TDT
recommends using preampliers which deliver ± 2.5 V or less. The table below lists the input
voltage ranges for the RA4LI headstage for either ± 1.5 V or ± 2.5 V power sources.
RA4LI Technical Specications
RA16LI - 16 Channel Headstage
The sixteen channel low impedance headstage (RA16LI) is a high quality, low- impedance
headstage designed for recording high channel count EEG's.
The RA16LI headstage is designed for low impedance electrodes and electrode caps with
input impedance between < 1 kOhm and 20 kOhm. Either headstage unit connects to the
Power Source Headstage Input Range
± 1.5 V ± 33 mV
± 2.5 V ± 80 mV
Input referred noise 0.1 uV RMS bandwidth 300-3000 Hz
0.3 uV RMS bandwidth 2-8000 Hz
Headstage Gain 20x
Highpass Filter 2.2 Hz
Lowpass Filter 7.5 kHz
Input Impedance 1e6 ohms
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Medusa preamplier's 25-pin connector. The simple interface to the RA16PA preamplier
makes it easy to connect your electrodes to our system.
An adapter is also available to connect a low impedance headstage to a PZ preamplier. See
Preamplier Adapters for more information. A built-in impedance checker can be used to test
each channel and the reference. Additional 20x gain on the headstage improves signal-to-noise
of low voltage signals.
Impedance Checking with the Low-Impedance Headstage
The impedance checker on the RA16LI provides a simple check of the channel impedance
relative to ground. To check the impedance level, press the button next to the channel
indicator. The highest-level light indicates the maximum impedance between the channel and
the ground. If all impedance lights are illuminated it is likely that one of the channels is not
properly connected. The (-) impedance button checks the impedance between the reference
and the ground.
Headstage Voltage Range
When using a TDT preamplier the voltage input range of the preamplier (PZ5, Subject
Interface, RA16PA) is typically lower than the headstage and must be considered the effective
range of the system. Also keep in mind that the output range of the headstage varies
depending on the power supply provided by the preamplier. PZ5 and Subject Interface supply
± 2.5 V. PZ2 and RA16PA preampliers supply ± 1.5V. Third party preampliers may vary. TDT
recommends using preampliers which deliver ± 2.5 V or less. The table below lists the input
voltage ranges for the RA16LI headstage for either ± 1.5 V or ± 2.5 V power sources.
Power Source Headstage Input Range
± 1.5 V ± 33 mV
± 2.5 V ± 80 mV
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RA16LI Technical Specications
Electrode Connector Pinout
The electrode connector is a 25-pin connector. Information on the pin inputs is provided below.
Input referred noise 0.1 uV RMS bandwidth 300-3000 Hz
0.3 uV RMS bandwidth 2-8000 Hz
Headstage Gain 20x
Highpass Filter 2.2 Hz
Lowpass Filter 7.5 kHz
Input Impedance 1e6 ohms
Pins 6, 14, 17, 18 and 19 are not connected.
Note
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RA16LI-D - 16 Channel Headstage with Differential
The RA16LI-D headstage is designed for fully differential recordings from low impedance
electrodes and electrode caps with input impedance between <1 kOhm and 20 kOhm. It
connects to the Medusa preamplier's 25-pin connector. The simple interface to the RA16PA
preampliers makes it easy to connect your electrodes to our system. An adapter is also
available to connect a low impedance headstage to a PZ preamplier. See DBF-MiniDBM Low
Impedance Headstage to PZ Preamplier (16-channels) for more information.
The differential inputs allow for improved common mode rejection on all channels. Because of
the increased complexity of the circuitry, the RA16LI-D does not have impedance checking. The
headstage connector is a DB44. The pin out diagram is shown below.
Pin Name Description Pin Name Description
1 A1 Analog Input Channels 14 NA Not Used
2 A2 15 GND Ground
3 A3 16 GND
4 A4 17 NA Not Used
5 Ref Reference 18 NA Headstage Detect
6 NA Not Used 19 NA
7 A5 Analog Input Channels 20 A6 Analog Input Channels
8 A7 21 A8
9 A9 22 A10
10 A11 23 A12
11 A13 24 A14
12 A15 25 A16
13 GND Ground
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Headstage Voltage Range
When using a TDT preamplier the voltage input range of the preamplier is typically lower
than the headstage and must be considered the effective range of the system. Check the
specications of your amplier for voltage range.
RA16LI-D Technical Specications
Pinout Diagram
Input referred noise 0.1 uV RMS bandwidth 300-3000 Hz
0.3 uV RMS bandwidth 2-8000 Hz
Headstage Gain 20x
Highpass Filter 2.2 Hz
Lowpass Filter 7.5 kHz
Input Impedance 1e6 ohms
Pins 1, 21-24 and 39 are not connected.
Note
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Pin Name Description Pin Name Description
1 NA Not Used 23 NA Not Used
2 A2 Analog Input 24 NA
3 D3 Differential Input 25 GND Ground
4 D5 26 GND
5 A5 Analog Input 27 D12 Differential Input
6 A7 28 A14 Analog Input
7 A8 29 A15
8 A9 30 D16 Differential Input
9 D9 Differential Input 31 D1
10 A10 Analog Input 32 A3 Analog Input
11 A11 33 D4 Differential Input
12 A12 34 GND Ground
13 D13 Differential Input 35 D6 Differential Input
14 GND Ground 36 D7
15 A16 Analog Input 37 D8
16 A1 38 GND Ground
17 D2 Differential Input 39 NA Not Used
18 A4 Analog Input 40 D10 Differential Input
19 GND Ground 41 D11
20 A6 Analog Input 42 A13 Analog Input
21 NA Not Used 43 D14 Differential Input
22 NA 44 D15
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