12ビット、RF サンプリング A/D コンバータ (ADC)" />
JAJSGI4B November 2018 – March 2021 ADC12DJ3200QML-SP
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The clocking subsystem of the ADC12DJ3200QML-SP has two input signals, device clock (CLK+, CLK–) and SYSREF (SYSREF+, SYSREF–). Within the clocking subsystem there is a noiseless aperture delay adjustment (tAD adjust), a clock duty cycle corrector, and a SYSREF capture block. Figure 7-3 shows the clocking subsystem.
The device clock is used as the sampling clock for the ADC core as well as the clocking for the digital processing and serializer outputs. Use a low-noise (low jitter) device clock to maintain high signal-to-noise ratio (SNR) within the ADC. In dual-channel mode, the analog input signal for each input is sampled on the rising edge of the device clock. In single-channel mode, both the rising and falling edges of the device clock are used to capture the analog signal to reduce the maximum clock rate required by the ADC. A noiseless aperture delay adjustment (tAD adjust) allows the user to shift the sampling instance of the ADC in fine steps in order to synchronize multiple ADC12DJ3200QML-SPs or to fine-tune system latency. Duty cycle correction is implemented in the ADC12DJ3200QML-SP to ease the requirements on the external device clock while maintaining high performance. Table 7-4 summarizes the device clock interface in dual-channel mode and single-channel mode.
MODE OF OPERATION | SAMPLING RATE VS fCLK | SAMPLING INSTANT |
---|---|---|
Dual-channel mode | 1 × fCLK | Rising edge |
Single-channel mode | 2 × fCLK | Rising and falling edge |
SYSREF is a system timing reference used for JESD204B subclass-1 implementations of deterministic latency. SYSREF is used to achieve deterministic latency and for multi-device synchronization. SYSREF must be captured by the correct device clock edge in order to achieve repeatable latency and synchronization. The ADC12DJ3200QML-SP includes SYSREF windowing and automatic SYSREF calibration to ease the requirements on the external clocking circuits and to simplify the synchronization process. SYSREF can be implemented as a single pulse or as a periodic clock. In periodic implementations, SYSREF must be equal to, or an integer division of, the local multiframe clock frequency. Equation 2 is used to calculate valid SYSREF frequencies.
where