Since the beginning of the HD digital series, SONY autofocus cameras have uniformly used LVDS display interface, why all switch to LVDS display interface? What are the advantages of LVDS interface for SONY autofocus cameras?
1. What is LVDS?
LVDS, namely Low Voltage Differential Signaling, is mainly a differential signal technology with low power consumption, low bit error rate, low crosstalk and low radiation. The core technology of LVDS mainly adopts a very low voltage swing high-speed difference to transmit data, and realizes point-to-point or point-to-many connection. The transmission medium is generally pcb connection or balance cable.
The LVDS output interface uses a very low voltage swing (about 350mV) to transmit data by differential on two PCB traces or a pair of balanced cables, that is, low-voltage differential signal transmission. Using LVDS output interface, the signal can be transmitted at the rate of several hundred Mbit/s on the differential PCB line or balanced cable. Due to the use of low voltage and low current drive mode, low noise and low power consumption are achieved.
Because LVDS differential signal technology reduces the concern for noise, a lower signal voltage amplitude can be used. This feature is very important and makes it possible to improve data transfer rates and reduce power consumption. Low driving amplitude means that the data can be reversed more quickly.
Since the driver is in constant current source mode, the power consumption almost does not change with frequency, and the power consumption of a single channel is very low. Therefore, this technology can provide very high data transmission rates as long as the length of a pair of parallel transmission lines is consistent enough and a good matching terminal impedance technology is provided at the receiving end to reduce the generation of reflected signals.
2. Working principle of LVDS
The source driver consists of a constant current source (usually about 3.5mA, the maximum is not more than 4mA) driving a pair of differential signal lines. The receiver itself at the receiver has a high DC input impedance, so almost all of the drive current flows through the 100Ω terminal matching resistor and generates a voltage of about 350mV at the receiver input. When the source drive state reverses, the direction of the current flowing through the matching resistor changes, resulting in a change of high and low logic state at the receiver.
In order to adapt to the common mode voltage changes in a wide range, generally, the LVDS receiver input stage also includes an automatic level adjustment circuit, which adjusts the common mode voltage to a fixed value, followed by a Schmitt trigger, and in order to prevent the Scdhmitt trigger instability, the design has certain hysteresis characteristics, The Schmitt post stage is the differential amplifier.
3. Technical advantages of LVDS
(1) High-speed transmission capacity: the transmission capacity of LVDS can reach up to 2Gbps;
(2) Low power consumption: LVDS is realized by a CMOS technology, which can effectively provide a low static power consumption state. In short, the power consumption of LVDS is a constant state, which is convenient to reduce the power consumption of the system.
(3) Strong anti-noise ability: the noise of LVDS is coupled to a pair of differential lines in a common mode, and subtracted from them at the same time. Then it can eliminate the noise very well;
(4) Strong anti-interference ability: differential transmission mode has strong anti-interference ability;
Why SONY autofocus camera to use LVDS display interface, its advantages are visible, using LVDS interface, SONY autofocus camera has high-speed transmission ability, low power consumption, strong anti-noise ability, anti-interference ability and other advantages. It is widely used in security monitoring, medical treatment, UAV, video conference, robot, intelligent transportation and other fields.
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