Thermal imaging & vision systems Low Frequency Noise Architecture
Ultralow noise reference in Silent Switcher 3 device
Feature
Figure 3. The low noise spectrum density in the next-generation LDO regulator: LT3045.
performance without spread spectrum on and keep excellent transient response.
White Noise
There are also many white noise sources in an ultrasound system, which leads to the background noise in ultrasound imaging. This noise mainly comes from the signal chain, clock, and power. Adding an LDO regulator at the analogue power pin of the analogue processing component is common now. ADI’s next-generation LDO
regulators feature around 1µV rms ultralow noise that covers current from 200mA to 3A. The circuit and specifications are shown in Figures 2 and 3.
PCB Layout
When designing a data acquisition board in an ultrasound system, it is easy to notice the trade-off between a high current power part and a highly sensitive signal chain part. Noise from switching power supplies will easily be coupled in the signal path trace and this is not easy to remove from data processing. The switching noise is usually
Benefit in Application
Same performance as an LDO regulator in terms of low f noise
Removing the necessity of post-LDO regulator while keeping the same image quality
Table 1. Silent Switcher Products Summary
generated from the switching input cap (Figure 4) and the hot loop generated by the up or down side switches. Adding a snubber circuit can help manage electromagnetic emission; however, it decreases efficiency at the same time. Silent Switcher architecture can help improve EMI performance and maintain high efficiency even at a high switching frequency.
limits (rather than the limit on the maximum intensity in the beam) that restrict the acoustic output of a transducer. Silent Switcher devices have the highest efficiency converting power (with a wide switching bandwidth up to 3MHz) to the different voltage domains of the digital probe. This means the power losses during power conversion are minimal. This helps the cooling system as there is not much additional power loss in form of heat.
SILENT SWITCHER µMODULE REGULATORS HELP A LOT
Silent Switcher µModule regulator technology is the best choice in ultrasound power rail design. It was
Figure 6. A copper pillar flip-chip package and its performance (LT8614) compared with a traditional bounding technique (LT8610).
Handheld digital probe Figure 4. Splitting a hot loop’s schematic.
Figure 5. A comparison of silent switching and nonsilent switching EMI performance.
Instrumentation Monthly April 2023
In addition to heating due to the absorption of ultrasound, the temperature of tissues near a transducer is strongly influenced by the temperature of the transducer itself. Ultrasound pulses are produced by applying an electrical signal to the transducer. Some electrical energy is dissipated in the element, lens, and backing material, causing transducer heating. Electronic processing of received signals in the transducer head may also result in electrical heating. Conduction of heat from the transducer face can result in a temperature rise of several degrees Celsius in superficial tissues. The maximum allowable transducer surface temperatures (TSURF) are specified in the IEC standard 60601-2-37. These are 50°C when the transducer is transmitting into air and 43°C when transmitting into a suitable phantom. This latter limit implies that skin (typically at 33°C) can be heated by up to 10°C. Transducer heating is a significant design consideration in complex transducers, and, in some circumstances, these temperature limits may effectively restrict the acoustic output that can be achieved. The safety standard IEC 60601-2-37 limits the temperature of the transducer surface to less than 50°C when running in air and to less than 43°C when in contact with a phantom at 33°C (for externally applied transducers) or at 37°C (for internal transducers). It is often these temperature
introduced to help improve EMI and switching frequency noise. Traditionally, we should take care of the circuit and layout design on the hot loop for each switching regulator. For a buck, as shown in Figure 4, a hot loop contains an input cap, a top side MOSFET, a bottom side MOSFET, and parasitic inductance introduced by wiring, routing, bounding, etc. Silent Switcher modules feature two major design approaches: firstly, as shown in Figure 4 and Figure 5, by creating an opposite hot loop, most of the EMI will be reduced due to bidirectional emission. Nearly 20dB will be optimized by this approach. Secondly, as shown in Figure 6, instead of direct bonding surrounding the chip, a copper pillar flip-chip package in a Silent Switcher module helps to reduce parasite inductance and optimize spike and dead time.
In addition, Silent Switcher technology offers high power density design and enables large current capability in a small package, keeping low theta JA and resulting in high efficiency.
Furthermore, many Silent Switcher µModule regulators also feature fix frequency, wide frequency range, and peak current architecture, enabling low jitter and fast transient response.
CONCLUSION
ADI’s Silent Switcher power µModule regulator and LDO products provide a total solution for
ultrasound power rail design, minimising system noise levels and switching noise. This helps to improve the image quality. They are also helpful to limit temperature increase and simplify PCB layout design complexities.
Analog Devices
www.analog.com 65
Switching Noise Harmonics
Silent Switcher technology plus Cu pillar package
Low EMI, low switching noise Fast switching frequency, tiny dead slot
High frequency with high efficiency Higher frequency, smaller filter size
High Thermal Performance
Silent Switcher
technology plus heat sink in package
High power density Smaller thermal resistance
Minimise degrading for the same current level
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82
