EEG Specific Features
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Figure 46. Scope Tab for Impedance Measurement at fDR/4 (DR = 4ksps)
7.3 External Calibration/Test Signals
ADS1299 generates a square wave test signal that can be used to check the functionality of the signal
chain (Refer to the datasheet for details). It also gives the user an option to provide external test signals
for calibration. For evaluation purposes with the EVM, the test signals can be provided directly to the
jumpers of the corresponding signals. SRB1 (pin2 of JP8), SRB2 (pin3 of JP7), BIASIN (Pin3 of JP6),
BIASREF (does not appear at a jumper, needs to be soldered to one side of R5).
7.3.1 Channel Inputs Disconnected
It may sometimes be required to provide a calibration or test signal to ADS1299 channel without the signal
being routed to the channel input pins (or electrodes). This can be accomplished by applying the positive
test signal to BIASIN pin and the negative test signal to BIASREF pin. The channel multiplexer must be
set as 010, BIASREF_INT bit in Config 3 register must be set to 0 to choose external BIASREF and
BIAS_MEAS bit in Config 3 must be set to 1. These multiplexer settings are illustrated in Figure 47.
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EEG Front-End Performance Demonstration Kit SLAU443–May 2012
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