CN105607683B - A kind of low pressure reference source realizes system - Google Patents

Abstract

A kind of low pressure reference source realizes system, be related to a kind of low pressure reference source realizes system, the existing low pressure reference voltage source category less than 1.2V of solution is few and internal resistance is high, during connecting valve capacitive load on reference voltage easy superposition interference burr, cause in the image that imageing sensor exports the problems such as be contaminated with stripe interference.Including a reference source and resistor voltage divider circuit, a RC passive low-pass filter circuits, power supply, the 2nd RC passive low-pass filter circuits, the active low-pass filter circuit of operational amplifier composition, series resistance, Large Copacity ceramic disc capacitor and imageing sensor.The topological structure that the present invention is followed using operational amplifier after the partial pressure of existing high voltage reference source, is fluctuated, using low-pass filter circuit reduction external interference using the Large Copacity ceramic disc capacitor reference voltage that reduces in parallel with the switching load electric capacity inside imageing sensor.

Description

A Realization System of Low Voltage Reference Source

technical field

The invention relates to a realization system of a low-voltage reference source, in particular to a realization system of a low-voltage reference source applied to a capacitive switching load of an image sensor.

Background technique

In today's image sensor applications, a variety of reference voltage sources are required, especially low voltage reference sources with voltages below 1.2V. Using a low-voltage reference source built inside the image sensor can not only improve reliability, but also reduce volume and weight. However, when the load is a switching capacitor, interference glitches will appear on the reference voltage, and the output image will be mixed with fringe interference. There are few types of low-voltage reference voltage sources with a voltage lower than 1.2V on the market, and most of them have high internal resistance, which cannot meet the application requirements of switched capacitor loads.

Therefore, the present invention provides a method and system for implementing a low-voltage reference source applied to a capacitive switching load of an image sensor.

Contents of the invention

The present invention solves the problem that the existing low-voltage reference voltage source lower than 1.2V has few types and high internal resistance, and when connecting a switch capacitive load, interference glitches are easily superimposed on the reference voltage, resulting in mixed stripe interference in the image output by the image sensor. , providing a realization system of a low-voltage reference source.

A realization system of a low-voltage reference source, including a reference source and a resistor divider circuit, a first RC passive low-pass filter circuit, a power supply, a second RC passive low-pass filter circuit, and an active low-pass filter composed of an operational amplifier circuit, series resistance, large-capacity ceramic chip capacitor and image sensor; the reference source and the resistance voltage divider circuit output reference voltage is input to the active active amplifier composed of the operational amplifier after the first passive low-pass filter circuit filters the noise of the reference voltage Low-pass filter circuit; the output voltage of the power supply is input to the active low-pass filter circuit formed by the operational amplifier after the noise is filtered by the second passive low-pass filter circuit; the output voltage of the active low-pass filter circuit formed by the operational amplifier is passed through The series resistor and large-capacity ceramic capacitor are sent to the image sensor;

The temperature coefficient of the reference source and the resistor divider circuit is less than The minimum output voltage value of the operational amplifier is less than V _REF -0.7, and the bandwidth is greater than The maximum output current is greater than The temperature coefficient of the active low-pass filter circuit composed of the operational amplifier is less than

In the formula, R is the resistance value of the series resistor, V _REF is the voltage of the reference source and the resistor divider circuit, n is the number of digits of the digital image output by the image sensor, T is the maximum temperature change around the image sensor when it is working, V _power is The output voltage of the power supply, I _max is the maximum operating current of the operational amplifier in the active low-pass filter circuit composed of the operational amplifier, and C1 is the capacitance of the large-capacity ceramic capacitor.

Beneficial effects of the present invention:

1. The present invention can meet the application requirements of multiple reference voltages of the image sensor, especially when it is lower than the conventional 1.2V, and does not need a specially customized chip, so the application is flexible.

2. The present invention uses a large-capacity ceramic capacitor in parallel with the switching load capacitor inside the image sensor to reduce the reference voltage fluctuation caused by the switching transient of the internal load capacitor, thereby reducing the requirements for parameters such as the internal resistance of the reference source and transient response characteristics.

3. The present invention uses a low-cost operational amplifier to form a second-order low-pass filter, which can not only reduce the output load of the reference source, but also reduce the influence of various interferences on the accuracy of the reference voltage.

Description of drawings

FIG. 1 is a schematic structural diagram of a realization system of a low-voltage reference source according to the present invention.

detailed description

Specific Embodiments 1. This embodiment is described in conjunction with FIG. 1 , a realization system of a low-voltage reference source,

The reference source and its resistor divider circuit generate the required reference voltage through voltage division, and the noise of the reference source is filtered by the first RC passive low-pass filter circuit; the voltage output by the power supply is used as the power supply of the operational amplifier, and the second The RC passive low-pass filter circuit filters the noise of the power supply to reduce the noise to the output of the operational amplifier; on the one hand, the active low-pass filter circuit composed of the operational amplifier filters out high-frequency noise, allowing low-frequency DC signals to pass through, and on the other hand uses The low output resistance characteristic of the operational amplifier improves its load capacity; the output voltage of the active low-pass filter circuit composed of the operational amplifier is sent to the image sensor after passing through a series resistor and a large-capacity ceramic capacitor.

In this embodiment, a large-capacity ceramic capacitor (capacity value C1) is used in parallel with the switch load capacitor inside the image sensor (capacity value C2) to reduce the reference voltage fluctuation caused by the switching transient of the internal load capacitor; C1> 10 ³ ×C2.

In this embodiment, the topology followed by the operational amplifier after voltage division of the high-voltage reference source is adopted; the input of the operational amplifier, that is, the first RC passive low-pass filter circuit uses a second-order RC low-pass filter to eliminate interference, requiring the first RC passive low-pass filter circuit to eliminate interference. The cutoff frequency f _a of the source low-pass filter circuit satisfies In the formula, the f _power supply is the switching frequency of the power supply; the operational amplifier itself and the surrounding resistors and capacitors form a second-order active low-pass filter; the output terminal resistor of the operational amplifier and the large-capacity ceramic capacitor at the load end form a first-order RC filter circuit , the cutoff frequency f _c of the first-order RC filter is required to satisfy The filter circuit powered by the operational amplifier, that is, the second RC passive low-pass filter circuit, adopts a first-order RC filter circuit, and its resistance value is required The cut-off frequency f _b of the second RC passive low-pass filter circuit satisfies

The temperature coefficient of the reference source is required to be less than The operational amplifier is required to be powered by a single power supply, and the lowest output voltage value is less than V _REF -0.7; the bandwidth is greater than The maximum output current is greater than The temperature coefficient is less than In the formula, R is the resistance value of the series resistor, V _REF is the voltage of the reference voltage source, n is the number of digits of the digital image output by the image sensor, T is the maximum temperature change around the image sensor when it is working, V _power is the power supply Output voltage, I _max is the maximum operating current of the operational amplifier.

The benchmark reference source described in this implementation mode adopts the benchmark source product of American AD Company. The two RC passive low-pass filter circuits use a second-order RC low-pass filter circuit composed of resistors and capacitors; the active low-pass filter circuit composed of operational amplifiers uses a second-order active low-pass filter circuit composed of JL124, resistors and capacitors; The series resistor is a metal film resistor with a small temperature coefficient; the power supply is a switching power supply; and the image sensor is a CMOS image sensor.

Claims (6)

1. An implementation system of a low-voltage reference source, including a reference source and a resistor divider circuit, a first RC passive low-pass filter circuit, a power supply, a second RC passive low-pass filter circuit, and an active low-pass filter circuit composed of an operational amplifier. pass filter circuit, series resistance, large-capacity ceramic capacitor and image sensor; its features are; The output reference voltage of the reference source and the resistor divider circuit is input to an active low-pass filter circuit composed of an operational amplifier after the noise of the reference voltage is filtered by the first passive low-pass filter circuit; The output voltage of the power supply is filtered by the second passive low-pass filter circuit and then input to the active low-pass filter circuit composed of the operational amplifier; The output voltage of the active low-pass filter circuit composed of the operational amplifier is transmitted to the image sensor through a series resistor and a large-capacity ceramic capacitor; The temperature coefficient of the reference source and the resistor divider circuit is less than The minimum output voltage value of the operational amplifier is less than V _REF -0.7, and the bandwidth is greater than The maximum output current is greater than The temperature coefficient of the active low-pass filter circuit composed of the operational amplifier is less than In the formula, R is the resistance value of the series resistor, V _REF is the voltage of the reference source and the resistor divider circuit, n is the number of digits of the digital image output by the image sensor, T is the maximum temperature change around the image sensor when it is working, V _power is The output voltage of the power supply, I _max is the maximum operating current of the operational amplifier in the active low-pass filter circuit composed of the operational amplifier, and C1 is the capacitance of the large-capacity ceramic capacitor. 2. the realization system of a kind of low-voltage reference source according to claim 1, is characterized in that, the cut-off frequency _f of described first RC passive low-pass filter circuit satisfies Where f _power supply is the switching frequency of the power supply. 3. The realization system of a kind of low-voltage reference source according to claim 1, characterized in that, the resistance value of the second RC passive low-pass filter circuit The cut-off frequency f _b of the second RC passive low-pass filter circuit satisfies 4. The implementation system of a low-voltage reference source according to claim 1, wherein the large-capacity ceramic capacitor is connected in parallel with the switching load capacitor inside the image sensor, and the large-capacity ceramic capacitor C1>10 ³ ×C2; C2 is the switching load capacitance inside the image sensor. 5. The realization system of a kind of low-voltage reference source according to claim 1, is characterized in that, the active low-pass filter circuit that described operational amplifier forms is formed second-order active low-pass filter by operational amplifier and resistor capacitor; The output terminal of the active low-pass filter circuit composed of the operational amplifier is connected with a resistor and forms a first-order RC filter circuit with a large-capacity ceramic capacitor at the load end. 6. The realization system of a low-voltage reference source according to claim 1, wherein the power supply is a single power supply.