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AD9215BCP-105EB Datasheet(PDF) 9 Page - Analog Devices |
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AD9215BCP-105EB Datasheet(HTML) 9 Page - Analog Devices |
9 / 28 page HSC-ADC-EVALB-SC/HSC-ADC-EVALB-DC Rev. 0 | Page 9 of 28 THEORY OF OPERATION The FIFO evaluation board can be divided into several circuits, each of which plays an important part in acquiring digital data from the ADC and allows the PC to upload and process that data. The evaluation kit is based around the IDT72V283 FIFO chip from Integrated Device Technology, Inc (IDT). The system can acquire digital data at speeds up to 133 MSPS and data record lengths up to 32 kB using the HSC-ADC-EVALB-SC FIFO evaluation kit. The HSC-ADC-EVALB-DC, which has two FIFO chips, is available to evaluate multichannel ADCs or demultiplexed data from ADCs sampling faster than 133 MSPS. A USB 2.0 microcontroller communicating with ADC Analyzer allows for easy interfacing to newer computers using the USB 2.0 (USB 1.1-compatible) interface. The process of filling the FIFO chip or chips and reading the data back requires several steps. First, ADC Analyzer initiates the FIFO chip fill process. The FIFO chips are reset, using a master reset signal (MRS). The USB microcontroller is then suspended, which turns off the USB oscillator and ensures that it does not add noise to the ADC input. After the FIFO chips completely fill, the full flags from the FIFO chips send a signal to the USB microcontroller to wake up the microcontroller from suspend. ADC Analyzer waits for approximately 30 ms and then begins the readback process. During the readback process, the acquisition of data from FIFO 1 (U201) or FIFO 2 (U101) is controlled via Signal OEA and Signal OEB. Because the data outputs of both FIFO chips drive the same 16-bit data bus, the USB microcontroller controls the OEA and OEB signals to read data from the correct FIFO chip. From an application standpoint, ADC Analyzer sends commands to the USB microcontroller to initiate a read from the correct FIFO chip, or from both FIFO chips in dual or demultiplexed mode. CLOCKING DESCRIPTION Each channel of the buffer memory requires a clock signal to capture data. These clock signals are normally provided by the ADC evaluation board and are passed along with the data through Connector J104 (Pin 37 for both Channel A and Channel B). If only a single clock is passed for both channels, they can be connected together by Jumper J303. Jumpers J304 and J305 at the output of the LVDS receiver allow the output clock to be inverted by the LVDS receiver. By default, the clock outputs are inverted by the LVDS receiver. The single-ended clock signal from each data channel is buffered and converted to a differential CMOS signal by two gates of a low voltage differential signal (LVDS) receiver, U301. This allows the clock source for each channel to be CMOS, TTL, or ECL. The clock signals are ac-coupled by 0.1 μF capacitors. Potentiometer R312 and Potentiometer R315 allow for fine tuning the threshold of the LVDS gates. In applications where fine-tuning the threshold is critical, these potentiometers can be replaced with a higher resistance value to increase the adjustment range. Resistors R301, R302, R303, R304, R311, R313, R314, and R316 set the static input to each of the differential gates to a dc voltage of approximately 1.5 V. At assembly, Solder Jumper J310 to Solder Jumper J313 are set to bypass the potentiometer. For fine adjustment using the pot, the solder jumpers must be removed, and R312 and R315 must be populated. U302, an XOR gate array, is included in the design to let users add gate delays to the FIFO memory chip clock paths. They are not required under normal conditions and are bypassed at assembly by Jumper J314 and Jumper J315. Jumper J306 and Jumper J307 allow the clock signals to be inverted through an XOR gate. In the default setting, the clocks are not inverted by the XOR gate. The clock paths described above determine the WRT_CLK1 and WRT_CLK2 signals at each FIFO memory chip (U101 and U201). The timing options above should let you choose a clock signal that meets the setup and hold time requirements to capture valid data. A clock generator can be applied directly to S1 and/or S3. This clock generator should be the same unit that provides the clock for the ADC. These clock paths are ac-coupled, so that a sine wave generator can be used. DC bias can be adjusted by R301/R302 and R303/R304. The DS90LV048A differential line receiver is used to square the clock signal levels applied externally to the FIFO evaluation board. The output of this clock receiver can either directly drive the write clock of the IDT72V283 FIFO(s), or first pass through the XOR gate timing circuitry described above. SPI DESCRIPTION The Cypress IC (U502) supports the HSC SPI standard to allow programming of ADCs that have SPI-accessible register maps. U102 is a buffer that drives the 4-wire SPI (SCLK, SDI, SDO, CSB1) through the 120-pin connector (J104) on the third or top row. J502 is an auxiliary SPI connector to monitor the SPI signals connected directly to the Cypress IC. For more information on this and other functions, consult the user manual titled Interfacing to High Speed ADCs via SPI at www.analog.com/hsc-FIFO. 1 Note that CSB1 is the default CSB line used. |
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