Hello. My name is Ume Onigiri. In the last issue, we studied the power supply for the Cyclone® IV E device used in the fabrication exercise. We supplied power to the device as we studied last time. Here is the schematic diagram.
We supplied 3.3 V to VCCIO for all I/O banks. I also supplied power to VCCA and VCCD_PLL, which I was not sure whether to supply power or not in the previous study. The board is now complete as shown in the schematic. When I turned on the power supply, the device operated normally. I thought I was safe for now.
However, later I realized that there was something I had to do with the power supply. It was described in the Pin Connection Guidelines for Cyclone IV devices.
VCCD_PLL must separate the power supply with a filter if it is powered from the same regulator as VCCINT. Usually, ferrite beads or similar devices must be used to separate the power supply. The figure below shows how this can be done.
Noise-sensitive power supplies must be separated from other power supplies. In this case, if the power supply is not separated, the noise may cause the PLL to malfunction. However, in my board this time, the device worked fine even though I did not separate the VCCD_PLL power supply. Why is this?
Luckily, I did not see anything wrong with the device because I did not use a PLL in my design configured for Cyclone IV E. The absence of a filter allows the PLL to operate without noise. Even if the PLL was affected by noise due to the absence of the filter, the signal in the design was not affected by the noise.
At any rate, we are relieved that there was nothing wrong with the device in this mistake. However, Ume Onigiri could not help but feel fearful that he might still be making a mistake that could threaten the device.
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