Kāhu Spectrometer ================= The Kāhu spectrometer is a multi-channel MR console with integrated gradient and shim controllers. The base model includes 2 transmit channels and 4 receive channels, while the upgraded model provides 16 receive channels. The :ref:`setup:Kāhu QuickStart Guide` explains the basics of how to set up the console. .. figure:: /images/kahu_console.jpg :width: 100% :align: center Kāhu spectrometer, 16 channel model Specifications -------------- Unless stated otherwise, these specifications apply to both the base and 16 channel models of Kāhu. General ^^^^^^^ .. list-table:: :header-rows: 0 :width: 100% :widths: 70 200 :align: center * - Power Supply - 24 V, 90 W * - Dimensions - 300 x 200 x 60 mm (Width x Depth x Height) * - Weight - 1.8 Kg RF Transmit ^^^^^^^^^^^ .. list-table:: :header-rows: 0 :width: 100% :widths: 70 200 :align: center * - Channels - 2 * - Frequency Range - 100 kHz - 140 MHz * - DAC Sample Rate - 400 MSPS * - Resolution - 16-bit * - Output Power - 0 dBm (0.63 Vpp) * - Output Impedance - 50 Ω * - Output Coupling - AC coupled * - Connector - SMA RF Receive ^^^^^^^^^^ .. list-table:: :header-rows: 1 :width: 100% :widths: 70 100 100 :align: center * - - Base Model - 16 Channel Model * - Channels - 4 - 16 * - Receive Processor - FPGA-based 32-bit quadrature - FPGA-based 32-bit quadrature * - Frequency Range - 100 kHz - 140 MHz [#rxf1]_ - 100 kHz - 140 MHz [#rxf1]_ * - Crosstalk, worst neighbor - -80 dB - -70 dB [#rxf2]_ * - Sample Rate - 100 MSPS - 50 MSPS * - Resolution - 16-bit - 14-bit * - Input Power Range - 10 dBm (2 Vpp) - 10 dBm (2 Vpp) * - Input Impedance - 50 Ω - 50 Ω * - Input Coupling - AC - AC * - Connector - SMA - MMCX .. [#rxf1] Subsampling is used for higher Nyquist zones. External bandpass anti-aliasing filters may be needed for optimal SNR. .. [#rxf2] Better than -80dB between non-neighboring channels, see :ref:`hardware/kahu:Crosstalk 16-Channel` Gradient Controller ^^^^^^^^^^^^^^^^^^^ .. list-table:: :header-rows: 0 :width: 100% :widths: 70 200 :align: center * - Channels - 4 * - Resolution - 16-bit * - Sampling Rate - 200 kSPS * - Voltage Range - ±10 V * - Max Current Output - 10 mA * - Output Type - Single ended * - Connector - BNC Shim Controller ^^^^^^^^^^^^^^^ .. list-table:: :header-rows: 0 :width: 100% :widths: 70 200 :align: center * - Channels - 16 * - Resolution - 16-bit * - Sampling Rate - 50 kSPS * - Voltage Range - ±5 V * - Max Current Output - 1 mA * - Output Type - Single ended * - Connector - High Speed I/O (Cable provided) Digital I/O ^^^^^^^^^^^ .. list-table:: :header-rows: 0 :width: 100% :widths: 70 200 :align: center * - General Purpose/Pulse Progammable Outputs - 28 * - Pulse Progam Trigger Inputs - 4 * - General Purpose Inputs - 4 Temperature Control ^^^^^^^^^^^^^^^^^^^ .. list-table:: :header-rows: 0 :width: 100% :widths: 70 200 :align: center * - Temperature sensor inputs - 2x PT100 inputs, with 24-bit ADC * - PID control outputs - 2x 5 V PWM outputs Embedded Platform ^^^^^^^^^^^^^^^^^ .. list-table:: :header-rows: 0 :width: 100% :widths: 70 200 :align: center * - Main Processor - Quad-core ARM Cortex-A53 * - Pulse Sequencer - FPGA-based real-time streaming engine * - Operating System - Linux * - Memory - 4 GB 64-bit DDR4 * - Ethernet - 1 Gbps * - USB - 4x USB 3 ports * - Other Features - Real Time Clock Detailed Description -------------------- .. todo:: Georgina: Add 16 channel Rx connector info GPIO ^^^^ The Kāhu console has 4 GPIO ports (see :ref:`setup:Connections`). Each port interfaces with 3.3 V TTL logic and has 7 output pins, 2 input pins and 1 ground pin. Following the pin numbering on the mating connector, the pin configuration for all ports is: .. list-table:: :header-rows: 2 :width: 60% :widths: 70 100 :align: center * - Part No. - `Molex 545991016 `_ * - Pin No. - Function * - 1, 2, 3, 4, 5, 6, 8 - Output * - 7, 9 - Input * - 10 - GND .. note:: **The metal shielding on the mating connector will need to be removed in order to access the solderable pins and see the printed pin numbering.** The image below shows the mating connector in GPIO port 3. .. figure:: /images/GPIO_mating_conn.JPG :width: 50% :align: center GPIO Connector For information on controlling the GPIO pins see the :ref:`matipo/usage:General Purpose Outputs` page. Interlock ^^^^^^^^^ Kāhu has 5 interlock output pins available on the *i-lock* connector, 1 for the shims and 1 for each gradient channel. These can be used to enable amplifier modules when a pulse sequence is active, and disable them when in standby. The interlock pins are not directly controllable, they will automatically be brought high for the entire duration of a pulse sequence. They will be brought low when the pulse sequence finishes or is aborted. .. figure:: /images/i_lock_connection.png :width: 50% :align: center Kāhu interlock connector pinout, viewed from the back .. list-table:: :header-rows: 2 :width: 60% :widths: 70 100 :align: center * - Cable Part No. - `SFSDT-07-28-G-20.00-SR `_ * - Pin No. - Function * - 1, 3, 5, 7, 9 - GND * - 2 - 5 V TTL Shim interlock Output * - 4, 6, 8, 10 - 5 V TTL Gradient interlock Outputs * - 11-14 - NC (reserved) Shim Controller ^^^^^^^^^^^^^^^ The pinout of the shim connector is as follows: .. figure:: /images/shim_connection.png :width: 50% :align: center Kāhu shim connector pinout, viewed from the back .. list-table:: :header-rows: 2 :width: 60% :widths: 70 100 :align: center * - Cable Part No. - `FCF8-20-01-L-12.00-S `_ * - Pin No. - Shim Channel Index * - 1 - 0 * - 2 - 1 * - 3 - 2 * - 4 - 3 * - 5 - 4 * - 6 - 5 * - 7 - 6 * - 8 - 15 * - 9 - 14 * - 10 - 13 * - 11 - 12 * - 12 - 11 * - 13 - 10 * - 14 - 9 * - 15 - 8 * - 16 - 7 * - 17 - 20 - NC .. caution:: **When plugging in the shim cable to Kāhu ensure the gold contacts are facing upwards.** Temperature control ^^^^^^^^^^^^^^^^^^^ Kāhu provides capability to monitor and control temperature through the *PT100* connector. Two sensor inputs can be connected and then used to automatically control the duty cycle of their respective PWM outputs to achieve a stable temperature. The two channels maybe be operated independently or in conjuction. Each PWM signal is 5 V and can be used to control a heater, fan, or peltier module. In the JupyterLab environment, the temperature can be monitored and the PID settings adjusted using the *System* dashboard app, see :ref:`dashboards:Temperature Monitor`. The pin configuration for the PT100 connector is: .. list-table:: :header-rows: 2 :width: 60% :widths: 70 100 :align: center * - Cable Part No. - `SFSDT-05-28-G-08.00-SR `_ * - Pin No. - Function * - 1 - PT100 2 Reference * - 2 - PT100 1 Reference * - 3 - PT100 2 + * - 4 - PT100 1 + * - 5 - PT100 2 - * - 6 - PT100 1 - * - 7, 8 - GND * - 9 - PWM 1, 5 V output * - 10 - PWM 2, 5 V output The diagram below illustrates the connector pinout and an example of how to connect a PT100 sensor to Kāhu. Note that the reference wire should connect at the sensor itself so that it is the same length/resistance as the '-' connection (3-wire PT100 configuration). .. figure:: /images/pt100_connections.png :width: 50% :align: center PT100 Sensor 1 Wiring Diagram Typical Performance Characteristics ----------------------------------- .. todo:: noise floor measurement, SNR?, frequency response? etc Crosstalk Measurement Setup ^^^^^^^^^^^^^^^^^^^^^^^^^^^ The crosstalk has been characterised by connecting Transmit channel 0 to each Rx channel in turn with a coaxial cable and transmitting a frequency sweep while acquiring on all Rx channels. Unconnected Rx channels were left unterminated for this test. .. figure:: /images/kahu_crosstalk_connection.png :width: 70% :align: center Crosstalk Measurement Setup A frequency sweep from 0 - 200 MHz was then transmitted, while acquiring signal on all Rx channels. Crosstalk 16-Channel ^^^^^^^^^^^^^^^^^^^^ The following plots show test results measured on the 16-channel Kāhu. Note that the sampling rate of the 16-channel Kāhu is 50 MSPS, which causes spikes at mutliples of 50 MHz due to the aliasing of the DC offset. .. figure:: /images/crosstalk_16/Rx_Coupling_Channel_0.png :width: 100% :align: center .. figure:: /images/crosstalk_16/Rx_Coupling_Channel_1.png :width: 100% :align: center .. figure:: /images/crosstalk_16/Rx_Coupling_Channel_2.png :width: 100% :align: center .. figure:: /images/crosstalk_16/Rx_Coupling_Channel_3.png :width: 100% :align: center .. figure:: /images/crosstalk_16/Rx_Coupling_Channel_4.png :width: 100% :align: center .. figure:: /images/crosstalk_16/Rx_Coupling_Channel_5.png :width: 100% :align: center .. figure:: /images/crosstalk_16/Rx_Coupling_Channel_6.png :width: 100% :align: center .. figure:: /images/crosstalk_16/Rx_Coupling_Channel_7.png :width: 100% :align: center .. figure:: /images/crosstalk_16/Rx_Coupling_Channel_8.png :width: 100% :align: center .. figure:: /images/crosstalk_16/Rx_Coupling_Channel_9.png :width: 100% :align: center .. figure:: /images/crosstalk_16/Rx_Coupling_Channel_10.png :width: 100% :align: center .. figure:: /images/crosstalk_16/Rx_Coupling_Channel_11.png :width: 100% :align: center .. figure:: /images/crosstalk_16/Rx_Coupling_Channel_12.png :width: 100% :align: center .. figure:: /images/crosstalk_16/Rx_Coupling_Channel_13.png :width: 100% :align: center .. figure:: /images/crosstalk_16/Rx_Coupling_Channel_14.png :width: 100% :align: center .. figure:: /images/crosstalk_16/Rx_Coupling_Channel_15.png :width: 100% :align: center Crosstalk 4-Channel ^^^^^^^^^^^^^^^^^^^ The 4-channel Kāhu crosstalk measurements are summarised below: .. todo:: add 4-channel kahu loopback crosstalk test plots .. list-table:: :header-rows: 1 :width: 100% :widths: auto :align: center * - Rx loopback channel - Rx 0 dB - Rx 1 dB - Rx 2 dB - Rx 3 dB * - 0 - 0 - -85 - -90 - -100 * - 1 - -85 - 0 - -100 - -105 * - 2 - -105 - -95 - 0 - -83 * - 3 - -100 - -100 - -80 - 0