Enhancing Power Distribution and Clock Stability for Improved Performance
In the realm of high-speed electronics, power supply jitter can significantly impact the performance of clocks and analog-to-digital converters (ADCs). Here are some key guidelines to help reduce jitter in these systems.
## Design Guidelines
### 1. High-Quality Crystal Oscillators Crystal oscillators are fundamental for generating stable and low-jitter clock signals. High-quality crystal units should be selected to ensure optimal performance.
### 2. Optimize Oscillation Circuits The design of the oscillation circuit accompanying the crystal is crucial. It should be optimized to work in harmony with the crystal unit to produce stable clock signals.
### 3. Implement Jitter Reduction Techniques Phase-Locked Loops (PLLs) can be used to reduce jitter in clock signals. Devices like the AD9543 offer a combination of analog and digital PLLs for effective jitter reduction.
### 4. Circuit Design Considerations Power supply noise management is essential. Minimize noise in the power supply by using noise filters or decoupling capacitors to prevent voltage fluctuations from affecting the clock or ADC circuits.
### 5. Board Design and Layout Minimize the length of signal traces on the PCB to reduce signal delay and scrubbing effects. Choose PCB materials that have low dielectric absorption to reduce signal distortion.
### 6. Testing and Calibration Manual tuning or automatic calibration methods can be used to ensure consistent performance.
High-speed clocks can be sensitive to the "cleanliness" of the power they receive. The noise paths to the clock include the noise presented at the input to the linear regulator, the regulator's internal noise, and current variations at the output of the linear regulator interacting with the impedance present at the output of the regulator.
A Picotest J2111A Current Injector is used to provide a narrow current pulse for external transient stimulus. The J2111A connected to the input of the linear regulator produces a jitter in the clock due to the finite impedance of the wall adapter and the regulator's PSRR.
The test setup for measuring clock phase noise and power supply jitter includes a low-cost, off-the-shelf, 3.3V, 125MHz CMOS SMD clock. The displayed average noise level (DANL) is approximately -143 dBc and the corresponding jitter is 441fS.
Replacing the wall adapter with a benchtop supply degrades the performance of the clock. The addition of a capacitor at the input of the linear regulator reduces the impedance and the resulting noise voltage to the clock. For instance, adding a 0.47uF ceramic capacitor at the input to the regulator reduces the input impedance at 2MHz and reduces the resulting jitter.
Many voltage regulator manufacturers are developing new lines of regulators (predominantly LDOs) with higher PSRR specifically for powering precision clocks and sensitive circuits. The replacement of the wall adapter with these regulators can further reduce power supply jitter.
Clock jitter interferes with the performance of digital circuits, including high-speed ADCs. By following these guidelines, engineers can design systems that effectively reduce power supply jitter, enhancing the performance of high-speed clocks and ADCs.
Controlled impedance is important when designing PCBs for high-speed clock systems to minimize signal delay and scrubbing effects, ensuring optimal performance.
In the realm of data-and-cloud-computing and technology, the reduction of power supply jitter in high-speed clock systems utilizing controlled impedance is crucial for the efficient operation of clocks and analog-to-digital converters (ADCs), particularly in high-speed electronics.
