““With the popularity of the Internet of Things, the number of sensors is increasing, and the role of op amps and comparators that detect and amplify the weak electrical signals of the sensors has become more and more important.” FAE Zhusha of ROHM Shanghai Technology Center Qin said.
As a bridge between analog and digital, the overall quality of the signal chain determines the accuracy of data transmission and the foundation needed for processing in the digital world.
For the signal chain, the first step is the signal amplifier and comparator. Their accuracy and processing speed determine the overall performance of the subsequent analog-to-digital conversion and processing.
“With the popularity of the Internet of Things, the number of sensors is increasing, and the role of op amps and comparators that detect and amplify the weak electrical signals of the sensors has become more and more important.” FAE Zhusha of ROHM Shanghai Technology Center Qin said.
The effect of noise
Noise is a central issue in analog circuit design, and it directly affects the amount of information that can be extracted from measurements, as well as the economic cost of obtaining the required information. For the amplifier, it will not only amplify the desired signal, but also amplify the noise, which will seriously affect the subsequent circuit system.
There are many factors that affect noise. Zhu Shaqin listed three important parameters, including input bias current, input offset voltage, and equivalent input noise voltage. Among them, the input bias current and the input bias current will generate an additional offset voltage drop at the input end, resulting in an offset error at the output end; the input offset voltage can be simply understood as the DC voltage error of the op amp, which may cause signal errors during high magnification amplification. Offset; the equivalent input noise voltage refers to the AC voltage error. When amplifying at high magnification, the signal component may be buried in the noise and cannot be detected.
Another part of the noise is related to electromagnetics, including EMI and EMS considerations. EMI refers to the noise generated inside the IC, while EMS refers to the IC’s immunity to external noise.
ROHM is improving various noise figures of products in terms of circuit design, process and packaging, and layout.
ROHM launches op amps and comparators with superior anti-jamming performance
Statistics show that in 2020, ROHM will ship a total of 500 million operational amplifiers and comparators, of which automobiles and industries account for about one-third. Zhu Shaqin said that with the increase in the number of automotive sensors, high-performance op amps or comparators are required on each data link, and the strong market demand also makes ROHM continue to develop corresponding new products.
The EMARMOUR series BD8758xYx-C has the dual advantages of ultra-low body, ultra-low noise and anti-EMI.
For the body’s ultra-low noise improvement, ROHM uses a CMOS process to replace the traditional bipolar process, thus achieving lower input bias current and lower power consumption. In addition, by improving the process and circuit design, flicker noise, thermal noise, etc. are reduced. At the same time, the size of the transistor is increased, and the effect of device fluctuation is reduced. And the optimized circuit design reduces the input offset voltage.
ROHM product noise index
Through a series of improvements, the new BD8758xYx-C product family can achieve a series of high-performance indicators, including: low equivalent input noise voltage 2.9nV/√Hz (@1kHz), 7.8nV/√Hz (@10Hz); low offset Voltage 950μV, 450μV, 150μV and low input bias current 0.5pA (Ta=25℃)
Excellent anti-EMI performance is another major feature of this series. Zhu Shaqin explained that EMARMOUR means to wear armor (ARMOUR), protected from external noise (ElectroMagnetic noise). This name is a registered trademark of ROHM and is only used for products with excellent immunity to interference with very little output voltage fluctuation in international immunity evaluation tests.
Zhu Shaqin said that the electromagnetic environment in automotive and industrial applications is relatively complex, and the anti-electromagnetic interference characteristics must meet the standards. Therefore, from the perspective of the design process, noise evaluation needs to be introduced at the beginning of the design of new products. However, for products that are generally not optimized for anti-EMI, it is difficult to evaluate at the initial stage, and can only be tested after the demo board is developed, which may lead to excessive noise and require rework or additional remedial measures. Choosing EMARMOURTM and other products with strong anti-noise ability can greatly reduce the user’s design time for EMI countermeasures, and at the same time, no additional CR filtering is required, reducing the use of peripheral components.
For the anti-noise characteristics, ROHM also made improvements in three aspects: circuit, layout, process and component structure. For the circuit, ROHM has developed a noise control circuit RF-IA (high-frequency impedance adjustment function), which effectively suppresses high-frequency interference. In terms of layout, ROHM set up a shielding structure around the noisy line, while improving layout interference and adjusting the impedance of the internal analog core. For the process and component structure, the parasitic capacitance is increased, thereby achieving stronger anti-interference.
EMARMOUR products have passed four tests including “Electronic Radiation Immunity Test ISO 11452-2″, “BCI Test ISO 11452-4”, “Proximity Radiation Immunity Test ISO 11452-9”, “DPI Test IEC 62132-4” An internationally accepted immunity evaluation test. Zhu Shaqin introduced that ordinary anti-EMI operational amplifiers generally only do “DPI tests”, and by taking filter countermeasures, they only have strong anti-noise capabilities in specific frequency bands. ROHM wanted to simplify the engineer’s design for EMC, while also ensuring that the product was more stable, so it passed four tests to achieve better immunity to interference.
Four kinds of tests and ROHM’s product indicators
In addition, for user simulation, ROHM provides a high-precision simulation model – “ROHM Real Model” SPICE model. Compared with the traditional SPICE model, the biggest advantage is that the simulation value is completely consistent with the actual IC value, and users can accurately conduct online simulation and design evaluation.
As shown in the table below, ROHM has taken the lead in mass-producing 1-channel and 2-channel products this time, and 4-channel products are under development. At present, the monthly production capacity of new products is 1 million (sample price is 300 yen/piece, excluding tax). This series supports the reliability standard “AEC-Q100” for automotive electronic products, realizing high reliability, and users can replace existing products with noise interference problems with confidence.