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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ADC12DJ3200QML-SP has a very high full-power input bandwidth to allow direct sampling of signals up to 10 GHz. In many cases, a transformer or balun is used to convert the front-end signal chain's single-ended signals to the differential signals ADC12DJ3200QML-SP requires. A 2:1 transformer will present a 100-Ω differential source impedance to the ADC from a single-ended 50-Ω source, however baluns or transformers with poor output return loss (not well matched to differential 100 Ω impedance) will result in frequency ripple in the ADC12DJ3200QML-SP frequency response. To improve the frequency ripple, resistive attenuators (Pi- or T-type) can be used to improve the output return loss of the drive component to dampen frequency response ripples at the cost of additional gain and drive strength in the preceding amplifier chain. Typically, 3 dB of attenuation is sufficient to dampen frequency response ripple introduced by poor output return loss. To be more general, achieving maximum frequency response flatness (as shown in Figure 6-68) with ADC12DJ3200QML-SP requires the output impedance of the device or passive component preceding the ADC12DJ3200QML-SP to be well matched to a differential, 100-Ω resistance. Additional impedance matching will not typically improve bandwidth.