Analyzing the innovative design of low dropout linear regulator (LDO) in camera applications

　   In recent years, with the continuous development of technologies such as 5G, AI, and biometrics, cameras have also been upgraded. Whether it is clarity, intelligence, or application scenarios, they are constantly being strengthened and enriched, such as telemedicine, remote office, AI temperature measurement, contactless identification, etc. For cameras, real-time clear image transmission is the basis of their operation, so product stability and clarity have become important indicators.

Mobile phone camera power supply solution

　　Generally speaking, a camera consists of five parts: housing (motor), lens, infrared filter, image sensor and flexible printed circuit board. As the core component of the camera, the image sensor is particularly susceptible to power interference, and power noise affects the ability of pixels to capture light normally, resulting in poor photo quality. As the most widely used mobile smart terminal, with the development of camera 3D sensing technology, the application of mobile phone cameras has expanded to scenarios such as biometrics, human-computer interaction, and AR experience. The growing demand for multiple cameras in mobile phones has brought great challenges to the design of power supplies.

Figure 1 Wei'an LDO mobile phone camera power supply solution

　　CMOS Image Sensor（图像传感器）需要三路电源（Core，Analog和I/O），其中2.8V为模拟电压，1.8V为I/O数字电压，1.2V为核电压。此时，通过维安WR0332外置低压差线性稳压器（LDO）为CMOS Image Sensor供电，可将集中在IC的热量分散开，抑制整个电路的发热量，实现高转换效率，有助于进一步降低手机摄像头模块的功耗。特别是应用于 AVDD时，优秀的纹波抑制能力1KHz@70dB，还能显著较少电源线干扰噪声，为CMOS图像传感器稳定供电。另外核电压部分，维安还开发设计了1.0V~1.2V输出的规格，可根据用户的需求选择不同的电压给Core供电。

　　For camera module applications that require low Vin, most current solutions use an LDO that converts an input of 1.8V or 1.6V to an output of 1.05V/1.1V. Vian's WR0513 can achieve a solution of 1.05V or 1.1V output with a 1.2V input power supply. With the increase in the number of mobile phone cameras, the amount of power that can be supplied by the battery and the space for installing the camera will be limited. Vian's WR0332/WR0341 and WR0513 series can solve the power consumption and power supply problems while taking into account the miniaturized package DFN-4 1mm*1mm*0.4mm.

Figure 2: Wei'an LDO low Vin input mobile phone camera power supply solution

#Weian Low Dropout Linear Regulator (LDO)

Security monitoring system power supply solution

　　Security video surveillance systems require real-time, continuous, and clear signals, and the amount of image signal data is very large. The analog video signals collected by analog cameras need to be encoded and compressed into digital signals so that they can be directly connected to network switching and routing equipment. Network cameras are generally composed of image/sound sensors, A/D converters, image/sound/controller network servers, external alarms, control interfaces, lenses, etc. They have very high requirements for system power supply, especially low noise in the analog part. At this time, LDO can be a perfect solution.

Figure 3 LDO security monitoring system power supply solution

　　Figure 3 shows the design of the system power management part. After the built-in DC/DC converter circuit converts the 12 V DC power supply into 5.0 V, multiple LDOs are required to provide outputs of different voltages to power the system's digital power supply, analog power supply, main chip core, and IO. Selecting Wei'an LDO to power the system can ensure high reliability while achieving low EMI and high-efficiency power circuits for the camera module.

#Weian Low Dropout Linear Regulator (LDO)

Key selection parameters and main product series

　　The main performance parameters of low-dropout linear regulators include dropout voltage, transient response, output accuracy, PSRR & Noise, etc. When powering CMOS Image Sensors and security monitoring systems, the parameters that are more sensitive to LDO are mainly PSRR and Noise. LDO noise mainly consists of two parts, one from the input front-end circuit and the other from the LDO itself. The former can suppress external noise interference by improving PSRR. The latter requires optimizing the LDO design or introducing a feedforward capacitor to optimize the output Noise.

Figure 4 Noise spectrum

　　If there is an audio signal processing application in the security monitoring system, then LDO is needed to provide bias voltage for the microphone. Since the weak signal of the microphone will be amplified and A/D (analog-to-digital) converted in the system, the difference of LDO noise in the audio range (20 Hz ~ 20 kHz) will have a great impact on the digital audio output after encoding and decoding.

Figure 5 PSRR @ 10 Hz to 10 MHz

　　The dynamic load range of CMOS Image Sensor is mainly between 10kHz and 1MHz. Therefore, at higher frequencies, high PSRR can improve image quality. In addition, PSRR is actively controlled by LDO; in the frequency range above 100 kHz, PSRR is more affected by passive devices in the system (capacitors, load current, PCB layout).

　　In the system circuit, the following points should be noted to improve the ripple suppression capability:

　　1. LDO selection: Select a suitable LDO based on the power supply PSRR requirements of the CMOS Image Sensor.

　　2. Choose the right capacitor. For some ceramic capacitors, the actual capacitance value varies with the DC bias and the operating temperature range of the application, so adding more capacitance does not necessarily improve performance.

　　3. Leave enough margin for voltage drop as much as possible. When the LDO works close to the dropout mode, there is not enough space to suppress the input ripple signal, which will reduce the PSRR.

　　4. Optimize PCB circuits. Ensure the rationality of board layout and the design of ground loop as small as possible to reduce crosstalk from external ripples.