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Innovative Design of LDO in Camera Applications

In recent years, with the continuous development of technology such as 5G, AI, biometrics, etc., the camera has also ushered in an upgrade iteration. Both clarity and degree of smartness of the camera are being strengthened; application scenarios are being enriched, including telemedicine, remote office, AI temperature measurement, contactless identification, and so on. For a camera, real-time clear image transmission is the basis of its operation, so the stability and clarity of the product has become an important indicator.



#WAYON LDO Mobile Phone Camera Power Supply Scheme

In general, a camera hardware consists of five parts: housing (motor), lens, IR filter, image sensor and flexible printed circuit board. The image sensor, as the core component of the camera, has items that are particularly susceptible to the interference from power supply. Power noise can affect the light capturing ability of pixels negatively, resulting in poor photo quality. As the most widely used smart mobile terminal, with the development of 3D sensing technology, mobile phone camera applications have been extended to biometric, human-computer interaction, AR experience and other scenarios. Moreover, the growing demand for multiple cameras in mobile phones has brought great challenges to the design of power supplies.


Figure 1. WAYON LDO Mobile Phone Camera Power Supply Scheme

CMOS Image Sensor requires three-way power supply (Core, Analog and I/O), among which, 1.2V is the core voltage, 2.8V is the analog voltage, and 1.8V is the I/O digital voltage. At this point, WAYON WR0332 external LDO supplies power to CMOS Image Sensor, which can disperse the heat concentrated in IC, suppressing the heat generation of the whole circuit. Thereby, high conversion efficiency can be achieved, which can further reduce the power consumption of the mobile phone camera module. Especially when applied to AVDD, the excellent ripple rejection capability of 1KHz@70dB also significantly reduces the power line interference noise and provides stable power supply for CMOS image sensors. In addition, WAYON has also developed and designed output specifications from 1.0V to 1.2V in the core voltage section, so that different voltage can be selected to power the Core according to user's need.

For camera module applications requiring low Vin, most of the available solutions in the market use LDOs with 1.6V or 1.8V input to 1.05V or 1.1V output. WAYON WR0513 can implement a 1.2V input power supply to provide a 1.05V or 1.1V output solution. With the increase in the number of cameras on a mobile phone, the amount of power that can be supplied by the battery and the space needed to install them are both limited. WAYON WR0332/WR0341 and WR0513 series can solve the problems of power consumption and power supply while taking into account the miniaturized package DFN-4 1mm*1mm*0.4mm.


Figure 2. WAYON LDO Low Vin Mobile Phone Camera Power Supply Scheme


#WAYON LDO  Security Surveillance System Power Supply Scheme

Security video surveillance systems require real-time, continuous and clear signals. Also, the volume of data of the image signal is very large, the analog video signal captured by the analog camera needs to be coded and compressed into digital signal, so that it can be directly connected to the network switching and routing equipment. Network cameras are generally composed of parts such as image/sound sensors, A/D converters, image/sound/controller network servers, external alarms, control interfaces, lenses and etc. Its requirements for system power supply are very high, especially in the analog part as low noise is required. In this case, LDO can be the perfect solution.


Figure 3. WAYON LDO Security Surveillance System Power Supply Scheme

Figure 3 shows the design of the system power management section. After the built-in DC/DC converter circuit converts the 12V DC power supply to 5.0V, multiple LDOs are required to provide outputs of different voltages to power the system's digital power supply, analog power supply, the core of the main chip, and the IOs. By choosing WAYON LDO, a low EMI and high efficiency power circuit for the camera module can be achieved while ensuring high reliability. 


#Key Parameters for WAYON LDO Selection and Main Product Series

The main performance parameters of LDO are leakage voltage, transient response, output accuracy, PSRR and Noise. By powering CMOS Image Sensor and security surveillance system, the crucial parameters of LDO are PSRR and Noise. Noise of LDO mainly comes from the pre-stage circuit at the input and LDO itself. The former can be reduced by increasing the PSRR to suppress external noise interference, while the latter can be decreased by improving the LDO design or introducing the feed-forward capacitors. 


Figure 4. Noise Spectrum Diagram

In security surveillance systems with audio signal processing applications, an LDO is required to provide bias voltage to the microphone. Since the weak microphone signal is amplified and A/D (analog-to-digital) converted in the system, the difference in Noise of the LDO in the audio range (20 Hz to 20 kHz) can have a large impact on the decoded digital audio output.


Figure 5. PSRR @ 10 Hz to 10 MHz

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

In the system circuit, the following points need to be taken into account to improve the ripple suppression capability:

1.Selection of LDO. Select the suitable LDO according to the requirement of CMOS Image Sensor for power PSRR.
2.Selection of a proper capacitor. For some ceramic capacitors, the actual capacitance value varies with the DC bias voltage and the operating temperature, so adding more capacitance will not necessarily improve the performance.
3.The margin of voltage dropout. When the LDO is operating close to Dropout mode, there is no sufficient space to suppress the input ripple signal, which will reduce the PSRR.
4.Optimization of PCB circuit. Ensure that the layout of the board is reasonable and the ground loop is designed to be as small as possible to reduce the external ripple crosstalk.


WAYON LDO Main Product Series


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