A circuit for reducing ambient light noise in an encoder

Abstract

The application provides a circuit for reducing ambient light noise in an encoder. In the encoder, the signal received by a photodiode array is often disturbed by ambient light. In the application, the photodiodes in the encoder are divided into two parts. The photodiodes in the PD array 1 (1) are used as the output signal of the circuit, and the signal of the photodiodes in the other part, the PD array 2 (2), provides a reference signal. The reference signal (4) is amplified by a TIA according to the proportion of the number of the two parts of the photodiodes, and then the high-frequency real signal in the reference signal is filtered out by a low-pass filter (5). Then, the output signal (3) is subtracted from the filtered and amplified reference signal (4) by a subtraction circuit (6), so that the ambient light noise is reduced and the real signal is retained. The application can be used for processing optical signals in optical encoder products and is also applicable to signal processing in other products with a photodetector array.

Description

Technical Field

[0001] This invention relates to a circuit for reducing ambient light noise in an encoder, applicable to photoelectric encoders or other photoelectric sensing devices composed of photodiode arrays, and belongs to the field of photoelectric sensor technology. Background Technology

[0002] An optical encoder is a photoelectric sensor that converts mechanical geometric displacement into pulses or digital signals. An optical encoder typically consists of a light source, a code disk, and a photodiode array that receives photoelectric signals. The code disk is driven by a moving mechanical device, which, in conjunction with the light source, modulates the energy distribution projected onto the photodiode array to generate pulses or digital signals. However, in practical applications, optical encoders do not necessarily operate in a completely sealed, light-proof environment. Besides natural ambient light signals, the light source may also project beams onto the photodiode array through non-ideal paths. Therefore, the photodiodes in an optical encoder often exhibit low-frequency DC noise. Because the photodiode array itself is very small and has a limited dynamic range, this DC noise can cause significant interference.

[0003] In the field of optoelectronic sensor technology, commonly used photodetectors in receiving pixels include photodiodes, avalanche photodiodes, and single-photon avalanche photodiodes. The most direct difference between these different types of photodetectors is the gain during photoelectric signal conversion. The single-photon avalanche photodiode has the highest gain among the three, followed by the avalanche photodiode, while the photodiode has the lowest gain. However, it is also the most affordable of the three. By arranging photodiodes in a special way to form an array, the function of an optoelectronic encoder can be realized. However, at the same time, various noises generated by the photodiode itself and during application also exist in the optoelectronic encoder system.

[0004] In everyday use, noise signals, such as ambient light and stray light, are often input into the photodiode array through various means. These noise signals are ultimately fed back into the circuit system as DC or AC noise, which can negatively impact encoder performance. For example, it can reduce the dynamic range of the photodiode in practical applications and cause phase errors in the encoder. Therefore, it is necessary to process these noise signals to ensure signal accuracy. Regarding the influence of ambient light on photoelectric sensors, Wu Jie, Wang Haiguang, Shao Mingshuan, and others proposed a method in CN209623858U that uses the pulsed light signal emitted by the MCU synchronous transmitter and the light signal received by the receiver to perform logical operations and extract the effective part of the received signal. Yue Xiaoguang, Shen Wei, Shen Xinjia, and others proposed another method in CN114637020B, which uses a pulse in a detection cycle as a reference and treats the signal returned by this pulse as DC noise in the system, thereby reducing its impact on the system. However, MCUs are expensive, and discarding a pulse in the encoder system can cause phase errors; therefore, neither of these methods is suitable for photoelectric encoders.

[0005] To address the above problems, this invention discloses a circuit for reducing ambient light noise in an encoder, which can be used in optical encoders and other photoelectric sensors with photodiode arrays. This invention designs the circuit to extract the signal generated by a portion of the photodiodes in the array, use it to calculate the DC noise caused by ambient light, and then subtract this DC noise to obtain a more ideal signal. Summary of the Invention

[0006] The purpose of this invention is to provide a circuit for reducing ambient light noise in an encoder, and the main considerations include:

[0007] 1. By dividing multiple photodiodes in a cycle into two or more groups and comparing them with each other.

[0008] 2. The number of photodiodes p and q in the two groups can form a certain ratio.

[0009] 3. The strength of each signal group is modulated by a resistor set according to the p:q ratio.

[0010] 4. Signals in some groups will be filtered out by a low-pass filter to remove DC noise.

[0011] 5. The DC component intensity is equal in each group of signals.

[0012] This invention achieves its function based on the following principles:

[0013] In the system, some photodiodes in the photodiode array in each cycle are set as output signals (3), and the number of them is p. The outputs of these p photodiodes are added together to form a preliminary output signal (3). This signal includes DC noise caused by ambient light and AC signal with a certain frequency.

[0014] In the system, a portion of the photodiodes in the photodiode array in each cycle are set as reference signals (4), and the number of these reference signals is q. The outputs of these q photodiodes are added together to form a preliminary reference signal (4). This signal includes DC noise caused by ambient light and AC signals with a certain frequency.

[0015] In this system, each section of the single-cycle photodiode array has a transimpedance amplifier that provides a certain gain to that section. The specific gain value is determined by the resistor connected in parallel with the transimpedance amplifier. In this system, each transimpedance amplifier is connected in parallel with a resistor of a certain resistance value, which has a certain proportional relationship. This proportional relationship is determined by the number of photodiodes in that group.

[0016] In the system, the resistance value of the resistor connected in parallel with the transimpedance amplifier when the output signal (3) passes through the transimpedance amplifier is R. g .

[0017] In the system, the resistance value of the resistor connected in parallel with the cross-amplifier when the reference signal (4) passes through the cross-impedance amplifier is R. d .

[0018] In the system, R g and R d The resistance values ​​have a certain ratio, which is determined by the number of photodiodes occupied by the two sets of signals. This ratio follows the formula:

[0019] R d / R g =p / q

[0020] In this system, after the reference signal is amplified by the cross-group amplifier, it passes through a low-pass filter to remove the AC component, retaining only the DC component as the overall DC noise of the system. The intensity of this noise is V. R .

[0021] In the system, after passing through a cross-group amplifier, the output signal is connected to an operational circuit. At this point, the output signal contains both DC noise and AC signal, where the intensity of the DC signal is V. R .

[0022] The output signal (3) and the reference signal (4) are connected to an operational circuit, such as a subtraction circuit. The output signal (3) can be used to subtract the reference signal (4), so that the output of the subtraction circuit is an AC signal that has been filtered out of DC noise. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the system structure of a circuit for reducing ambient light noise in an encoder. The system mainly consists of PD array 1 (1) and PD array 2 (2), two circuits with output signal (3) and reference signal (4) respectively, a subtraction circuit (6) and its output terminal. The output signal (3) and the reference signal (4) are both passed through a TIA connected in parallel with a resistor, and the reference signal (4) is also filtered by a low-pass filter (5).

[0024] Figure 2 This is a specific implementation of a circuit for reducing ambient light noise in an encoder. The entire system consists of a PD array composed of 5 photodiodes. The PD array is divided into two parts: one part consists of p photodiodes, the sum of the outputs of these p photodiodes constitutes the output signal (3), where p = 4; the other part consists of q photodiodes, the sum of the outputs of these q photodiodes constitutes the reference signal (4), where q = 1; the reference signal (4) is amplified by a TIA and then passed through a low-pass filter (5) to have an intensity of V. R The DC component; the output signal (3) amplified by TIA has an intensity of V R The DC component and the effective signal; the subtraction circuit (6) subtracts the two input signals to remove the DC component from the signal; in this process, in order to make both signals input to the subtraction circuit (6) have a strength of V R The DC components, Rg and Rd, have a specific ratio that follows:

[0025]

[0026] Figure 3 A specific implementation of a circuit for reducing ambient light noise in an encoder. The entire system consists of a PD array composed of 7 photodiodes. The PD array is divided into two parts: one part consists of p photodiodes, the sum of the outputs of these p photodiodes forming the output signal (3), where p = 5; the other part consists of q photodiodes, the sum of the outputs of these q photodiodes forming the reference signal (4), where q = 2; the reference signal (4) is amplified by a TIA and then passed through a low-pass filter (5) to have an intensity of V. R The DC component; the output signal (3) amplified by TIA has an intensity of V RThe DC component and the effective signal; the subtraction circuit (6) subtracts the two input signals to remove the DC component from the signal; in this process, in order to make both signals input to the subtraction circuit (6) have a strength of V R The DC components, Rg and Rd, have a specific ratio that follows:

[0027] Detailed Implementation

[0028] Example 1:

[0029] The entire system consists of a PD array composed of 5 photodiodes. The PD array is divided into two parts: one part consists of p photodiodes, the sum of the outputs of these p photodiodes constitutes the output signal (3), where p = 4; the other part consists of q photodiodes, the sum of the outputs of these q photodiodes constitutes the reference signal (4), where q = 1; the reference signal (4) is amplified by TIA and then passed through a low-pass filter (5) to have an intensity of V. R The DC component; the output signal (3) amplified by TIA has an intensity of V R The DC component and the effective signal; the subtraction circuit (6) subtracts the two input signals to remove the DC component from the signal; in this process, in order to make both signals input to the subtraction circuit (6) have a strength of V R The DC components, Rg and Rd, have a specific ratio that follows:

[0030]

[0031] Example 2:

[0032] Figure 3 A specific implementation of a circuit for reducing ambient light noise in an encoder. The entire system consists of a PD array composed of 7 photodiodes. The PD array is divided into two parts: one part consists of p photodiodes, the sum of the outputs of these p photodiodes forming the output signal (3), where p = 5; the other part consists of q photodiodes, the sum of the outputs of these q photodiodes forming the reference signal (4), where q = 2; the reference signal (4) is amplified by a TIA and then passed through a low-pass filter (5) to have an intensity of V. R The DC component; the output signal (3) amplified by TIA has an intensity of V R The DC component and the effective signal; the subtraction circuit (6) subtracts the two input signals to remove the DC component from the signal; in this process, in order to make both signals input to the subtraction circuit (6) have a strength of V R The DC components, Rg and Rd, have a specific ratio that follows:

[0033]

Claims

1. A circuit for reducing ambient light noise in an encoder, characterized in that: This circuit is suitable for a specific incremental output signal in an optical encoder, where the output signal corresponds to photoelectric signals generated by multiple photodiodes. Among these photoelectric signals, some are generated by the encoder receiving the corresponding light source, while others are generated by ambient light. The photoelectric signals generated by ambient light can interfere with the encoder's output signal, thereby affecting the system's sensitivity and dynamic range parameters. By dividing the photodiodes in the PD array into different groups, amplifying their signal strengths according to a certain ratio, and then subtracting them, a high-quality signal with ambient light noise removed can be obtained. The N photodiodes used to output the same signal need to be divided into two groups. One group of photodiodes with a quantity of p is used as PD array 1 (1) to output the signal (3), and the other group of photodiodes with a quantity of q is used as PD array 2 (2) to output the reference signal (4). N, p, and q are all positive integers, and p and q are both less than N. The values ​​of p and q conform to the following formula: , The output signal (3) from p photodiodes is first connected to a transimpedance amplifier (TIA). To modulate the signal, a resistor with a resistance of is connected in parallel to this transimpedance amplifier, so that the intensity of the DC component of the output signal branch is . ; The reference signal (4) output by the q photodiodes is first connected to a transimpedance amplifier (TIA). In order to modulate the signal, a resistor with a resistance of is connected in parallel to this transimpedance amplifier, so that the intensity of the DC component of the reference signal branch is . ; After the reference signal is amplified by the cross-amplifier, it passes through a low-pass filter to remove the AC component, retaining only the DC component as the overall DC noise of the system. The intensity of this noise is... ; After passing through the cross-group amplifier, the output signal is connected to an operational circuit. At this point, the output signal contains both DC noise and AC signal, with the DC signal strength being... ; The output signal and the reference signal are connected to an arithmetic circuit, which is a subtraction circuit. The output signal (3) is subtracted from the reference signal (4). The output of the subtraction circuit is an AC signal that has been filtered out of DC noise.

2. A circuit for reducing ambient light noise in an encoder according to claim 1; characterized in that: The resistor connected in parallel to the TIA through which the output signal passes The resistor connected in parallel with the TIA through which the reference signal passes. The resistance values ​​are in a certain proportion to adjust the signal strength in the middle of the two branches, so that the DC component signal strength in the two branches is... ,in and The proportional relationship of resistance values ​​is determined by the following formula: 。

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