There are some test challenges in using oscilloscope based solutions to test power supply and signal integrity, which must be considered and solved to achieve the best performance.
First, let’s define what power and signal integrity are. Signal integrity (SI) analysis focuses on the BER performance of transmitter, reference clock, channel and receiver. Power integrity (PI) focuses on the technology that power distribution network (PDN) provides constant, clean power supply and low impedance return path. Si and PI have extensive interdependence. PDN can cause noise and jitter. Circuit design and components, such as chip packaging, pins, wires, vias, connectors, etc., will affect the impedance of PDN, thus affecting the quality of power supply.
We know that the introduction of noise and jitter from the power supply will lead to the bit error rate in the high-speed serial network, which will at least reduce the efficiency of the embedded system. In the worst case, it may lead to wrong bits or wrong data in the mission critical environment.
Power integrity is more than just keeping the voltage in the right range. Power integrity is to ensure that the power supply applied to the circuit or equipment is suitable for the expected performance of the circuit or equipment. Its purpose is to maintain the power quality from power supply to power consumption, and to achieve acceptable power integrity means that the noise level is within the specified allowable range.
This becomes more and more important as electrical components are required to perform more functions on smaller circuit boards. With the continuous reduction of size and the increase of complexity, embedded systems are getting closer to the power delivery path or power integrity components.
In the process of testing and analyzing power integrity and signal integrity, it is very important to solve some key problems. Here, we solve five of them.
1. Filter out the ripple in AC-DC power conversion. Here, designers need to maintain the best power quality to ensure that any switch ripple contained will not be leaked to the downstream, while maintaining high efficiency. Designers must ensure high efficiency / low noise DC conversion to power the whole PDN and keep PSN to a minimum.
2. DC to DC power conversion. At this stage of the power supply, the designer supplies power to the last stage or point of load (POL) components. The most sensitive power supply includes high-speed ADC, FPGA core and digital signal processor (DSP). An embedded design may have more than 1000 voltage and ground planes to transfer power between components. It is also a challenge to deal with different loads at different voltage levels.
3. The influence of measurement system on the results. This includes the range in use, different measurement methods, probes, and any adapter used in front of the probe tip. It is very important to understand these so that we can know their impact on the measurement. One example is that adding any probe lead will reduce the total bandwidth of the measurement system. There is a trade-off between the convenience and performance of the probe connection, so it is important to understand the bandwidth and common mode rejection of any connector.
4. Signal integrity and power integrity. Since both power integrity and signal integrity affect each other, it is very important to understand how they affect each other. The noise of one will affect the other, and you need to understand the differences between these measurements to determine the root cause of the noise source. Designers need to correlate the ripple of sensitive power supply in time domain and frequency domain.
5. The response of the device in the whole frequency range. All devices will change in a frequency range. It is very important to understand the impedance and the change of components under power supply in this frequency range. This is used to determine the basic resonant frequency required to maintain the power supply.
Signal integrity and power integrity are often considered separate disciplines, but we have seen that a good understanding of their differences is needed to address these five key challenges. Mso6b series mixed signal oscilloscopes can be used as such a necessary tool to meet the testing needs of both disciplines in an easy-to-use touch screen environment. To learn more about jitter analysis, watch our webinar on diagnosing power and signal integrity issues.