Supplement: Power
LC fi lter circuit under simulation.
An LC fi lter circuit using a low-power signal bead that is for the rated current of the device.
LC peaking at 1.4 dB.
integrity and reliability. By understanding the dynamics of power supply noise and implementing these noise mitigating solutions correctly, engineers can enhance the performance and dependability of electronic systems, ensuring they meet necessary standards and function as intended.
Learn more timing essentials in ‘Common Timing Issues and Solutions’:
https://learning.sitime.com/explore/ common-timing-issues-and-solutions
Overshoot resolution: Use a signal/power supply ferrite bead.
ESR capacitors and strategic placement that is very close to the oscillator VDD pin to mitigate noise effectively. Additionally, a bulk capacitor (~10µF) placed a few millimetres away suppresses low-frequency noise for precision clock sources such as temperature-compensated oscillators (TCXOs) and oven-controlled oscillators (OCXOs), ensuring optimal stability in noisy environments.
2. Choose appropriate inductive elements for power supply LC filters, rated for the device current. An incorrect choice of the inductive element in a power supply inductor- capacitor (LC) filter can not only impact performance, but it can also cause permanent damage to timing devices. A CMOS device power supply has a maximum rating of 4V, so it’s important to choose the appropriate ferrite bead low-pass filter to suppress resonance peaking and transient overshoot. The following simulation demonstrates a circuit with an actual model of a ferrite bead, bypass capacitor parasitic and transmission line characteristics. It demonstrates how an incorrect bead – such as one for high-current applications
www.cieonline.co.uk
– can deliver an unfavourable frequency response. This example uses a 600 ohm ferrite bead at 100 MHz and reached ~9dB peaking at around 25 kHz. Because of the transient overshoot response, the power supply of the timing device will have a voltage at ~4V. On power up, depending on the supply ramp rate, the LC circuit can cause an overshoot of up to 5.1V, damaging the oscillator. Using a low-power signal/power supply ferrite-bead, 120 ohm at 100 MHz, reduced LC peaking from 9dB to 1.4dB at ~50kHz. LC transient overshoot reduced from 5.1 to 3.8V with power supply rise time of 5μs. This demonstrates the importance of choosing a low power signal bead that is for the rated current of the device with lower impedance (Z) at 100 MHz.
Managing power supply noise for optimal system performance Managing power supply noise is essential for the optimal function of system clocks. Employing low ESR capacitors, strategically choosing the ferrite bead in LC filters, and ensuring proper component placement are key techniques to mitigate noise and maintain timing component
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