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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