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Created page with "The signal generator provides the reference sinusoidal signals for the field generator emitter coils. =Waveform generator= The waveform generator provides the reference sinus..."
The signal generator provides the reference sinusoidal signals for the field generator emitter coils.
=Waveform generator=
The waveform generator provides the reference sinusoidal signals for each emitter coil of the field generator. The generator comprises of a single Analog Devices [http://www.analog.com/media/en/technical-documentation/data-sheets/AD9833.pdf AD9833] programmable integrated circuit which provides a reference sinewave at a desired frequency. The IC is programmed over the SPI bus using a microcontroller.
==Overview==
The AD9833 synthesises the reference sine waves for each emitter coil. The integrated circuit is programmed over the serial peripheral interface (SPI) using a microcontroller.
==Programming the AD9833==
On powering up the IC needs to be configured to output the required frequency. The AD9833 contains a set of registers which can be written over the SPI interface.
The desired frequency register value (denoted 'FREQREG' in the datasheet) can be found using the following formula:
<math display="block">\text{FREQREG} = \frac{f_{OUT}\times 2^{28}}{f_{MCLK}}</math>
where <math>f_{OUT}</math> is the desired output frequency of the AD9833 and <math>f_{MCLK}</math> is the frequency of the master clock signal input provided by a clock driver.
For example, to program an output frequency of 20.5kHz using a 6MHz master clock signal:
<math display="block">\text{FREQREG} = \frac{20500\times 2^{28}}{6\times10^6} = DFEA2_{16}=11011111111010100010_{2}</math>
The full programming sequence is detailed in the datasheet and [http://www.analog.com/media/en/technical-documentation/application-notes/AN-1070.pdf application note]. Typically a microcontroller platform (for example [https://www.arduino.cc/ Arduino] or [http://energia.nu/ MSP430] is used to program each waveform generator when the system powered-on.
=Variable gain stage=
The gain stage amplifies the output of the sinewave generator. The output of the AD9833 is capacitively coupled to the input of the [http://www.ti.com/product/TL081 TL081], a general purpose op-amp. The TL081 is configured with a potentiometer to allow the gain of the amplifier to be adjusted.
<math>R1</math> and <math>R2</math> form the feedback resistor network which controls the gain of the amplifier. The voltage gain is calculated using the following formula:
<math display="block">A=1+\frac{R_2}{R_1}</math>
<math>R2</math> is potentiometer and can be varied to meet the gain requirements of the system. Detailed information regarding the circuit design and layout can be found in the schematics.
=Waveform generator=
The waveform generator provides the reference sinusoidal signals for each emitter coil of the field generator. The generator comprises of a single Analog Devices [http://www.analog.com/media/en/technical-documentation/data-sheets/AD9833.pdf AD9833] programmable integrated circuit which provides a reference sinewave at a desired frequency. The IC is programmed over the SPI bus using a microcontroller.
==Overview==
The AD9833 synthesises the reference sine waves for each emitter coil. The integrated circuit is programmed over the serial peripheral interface (SPI) using a microcontroller.
==Programming the AD9833==
On powering up the IC needs to be configured to output the required frequency. The AD9833 contains a set of registers which can be written over the SPI interface.
The desired frequency register value (denoted 'FREQREG' in the datasheet) can be found using the following formula:
<math display="block">\text{FREQREG} = \frac{f_{OUT}\times 2^{28}}{f_{MCLK}}</math>
where <math>f_{OUT}</math> is the desired output frequency of the AD9833 and <math>f_{MCLK}</math> is the frequency of the master clock signal input provided by a clock driver.
For example, to program an output frequency of 20.5kHz using a 6MHz master clock signal:
<math display="block">\text{FREQREG} = \frac{20500\times 2^{28}}{6\times10^6} = DFEA2_{16}=11011111111010100010_{2}</math>
The full programming sequence is detailed in the datasheet and [http://www.analog.com/media/en/technical-documentation/application-notes/AN-1070.pdf application note]. Typically a microcontroller platform (for example [https://www.arduino.cc/ Arduino] or [http://energia.nu/ MSP430] is used to program each waveform generator when the system powered-on.
=Variable gain stage=
The gain stage amplifies the output of the sinewave generator. The output of the AD9833 is capacitively coupled to the input of the [http://www.ti.com/product/TL081 TL081], a general purpose op-amp. The TL081 is configured with a potentiometer to allow the gain of the amplifier to be adjusted.
<math>R1</math> and <math>R2</math> form the feedback resistor network which controls the gain of the amplifier. The voltage gain is calculated using the following formula:
<math display="block">A=1+\frac{R_2}{R_1}</math>
<math>R2</math> is potentiometer and can be varied to meet the gain requirements of the system. Detailed information regarding the circuit design and layout can be found in the schematics.