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Employ low output noise regulator for data acquisition

Posted: 12 Sep 2014 ?? ?Print Version ?Bookmark and Share

Keywords:FPGA? data converters? linear regulators? switching regulator? LTM8028?

The sampling process produces 250kHz spurs at base band. As a result, the SINAD drops to 71.84dB, around 4dB compared to an LDO. This reduces the LTC2185 to nearly 12bit performance. In demanding applications where tenths of dBs are significant, losing 4dB of SINAD because of a noisy regulator is unacceptable. In addition to degrading the SINAD of the ADC, these spurs may land on neighbouring channels or on other signals of interest, making it impossible to receive meaningful data from those channels. With the LTM8028, only a few extraneous spurs exist near the desired frequency and the SINAD performance is only 0.03dB worse than the LDO baseline. The spurious content that was very pronounced in the spectrum of the switching regulator is virtually eliminated. As a result, there will not be any performance degradation of the LTC2185 when using a LTM8028 regulator.

Figure 3: Noise test schematic using different supplies to power 16bit LTC2185 ADC.

Figure 4: 32k-Point FFT, fIN = 70.3MHz, C1dBFs, 100Msps, using CMOS clock drive.

The LTM8028?Module regulator combines a linear regulator and a switching regulator to form a DC/DC converter with minimal power loss, low noise and UltraFast transient response in a 15mm x 15mm x 4.92mm BGA package.

About the author
Willie Chan is Senior Product marketing Engineer, Power?Module Products, Linear Technology.

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