CN105163048A - Dynamic vision sensor based on amplifier multiplexing - Google Patents

Abstract

The present invention relates to the field of integrated circuits. In order to provide a sensor that adopts a multiplexing structure to realize continuous monitoring of photocurrent and quantitative readout of light intensity, the technical solution adopted by the present invention is a dynamic visual sensor based on amplifier multiplexing, photoelectric The diode PD is connected to the source stage of the logarithmic tube Mfb, and an amplifier A1 is added between the gate stage and the source stage of Mfb to form a negative feedback loop, which is used to logarithmically convert the photocurrent detected by the photodiode into a voltage; The gate of the logarithmic tube Mfb is also connected to the capacitor C1, and a switch SW3 is added between the capacitor C1 and the amplifier A2; one end of the switch SW4 is connected to the input end of the amplifier A2, and the other end is connected to the reference voltage Vref; the capacitor C2 and the reset switch SW2 are respectively connected to the amplifier A2 is connected in parallel, and the capacitor C3 is connected in series with the switch SW1 and connected to both ends of the amplifier A2. The invention is mainly applied to the design and manufacture of integrated circuits.

Description

Dynamic Vision Sensor Based on Amplifier Multiplexing

technical field

The invention relates to the field of integrated circuits, in particular to a dynamic visual sensor for quantitative readout of light intensity by means of amplifier multiplexing. Specifically, it relates to dynamic vision sensors based on amplifier multiplexing.

technical background

Dynamic Vision Sensor (DynamicVisionSensor, DVS) is a new type of CMOS (ComplementaryMetalOxideSemiconductor, Complementary Metal Oxide Semiconductor) image sensor, the basic structure of its pixel is shown in Figure 1, consisting of photodiode PD, logarithmic tube Mfb, amplifier A1, A2, capacitor C1, capacitor C2, switch RST, ON comparator, OFF comparator and logic module logic. The specific working method is as follows:

The photodiode PD generates a photocurrent Iph due to being illuminated, and the Iph is converted into a corresponding optical signal voltage Vp through the logarithmic tube Mfb. The function of the amplifier A1 is to form a negative feedback loop, so that Vp can respond to the change of Iph in time. The conversion relationship between Vp and Iph is

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&kappa;</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; .</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; l</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}\mathrm{<span\; class="notranslate">\; h</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>$

Where κ represents the subthreshold slope factor of Mfb, VS represents the source voltage of the logarithmic tube Mfb, UT represents the thermal voltage, and I0 represents the constant reference current of the photodiode PD. Capacitors C1 and C2, amplifier A2 and switch RST form a switched capacitor amplifier. When the switch RST is turned off, the change value ΔVdiff of the voltage Vdiff at the output terminal of the amplifier changes in proportion to the change value ΔVp of the voltage Vp at the input terminal of the amplifier, that is,

${\mathrm{<span\; class="notranslate">\; \&Delta;V</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; f</span>}\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; \&Delta;V</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}$

Therefore, DVS can monitor the change of Vp in real time: if ΔVdiff reaches the set change threshold Vth, ON (usually a negative value), the ON comparator outputs a pulse, which is called an ON event; if ΔVdiff reaches If the set change threshold Vth,OFF (usually a positive value), the OFF comparator outputs a pulse, it is called an OFF event. When an event occurs, the logic module outputs the event and controls the switch RST to close, clears the event and performs a reset process. After the reset is completed, the switch RST is turned off, and this event cycle is completed, and the DVS will start a new round of monitoring process.

From the working principle of DVS above, it can be seen that the traditional DVS can only monitor the continuous change of photocurrent to generate ON/OFF event pulses that characterize its changing nature, but it does not have the function of quantifying and reading out the light intensity information itself. . If DVS is required to obtain light intensity information while detecting changes in light intensity, it is necessary to introduce an additional quantitative readout circuit into the DVS pixel structure.

Contents of the invention

In order to overcome the deficiencies of the prior art, a sensor that adopts a multiplexing structure to realize continuous monitoring of photocurrent and quantitative readout of light intensity is provided. The sensor, the photodiode PD is connected to the source of the logarithmic tube Mfb, and an amplifier A1 is added between the gate and source of Mfb to form a negative feedback loop, which is used to logarithmically convert the photocurrent detected by the photodiode is the voltage; the gate of the logarithmic tube Mfb is also connected to the capacitor C1, and a switch SW3 is added between the capacitor C1 and the amplifier A2; one end of the switch SW4 is connected to the input end of the amplifier A2, and the other end is connected to the reference voltage Vref; the capacitor C2 and the reset switch SW2 They are respectively connected in parallel with the amplifier A2, and the capacitor C3 is connected in series with the switch SW1 and connected to both ends of the amplifier A2; the output of A2 is respectively connected with the ON comparator and the OFF comparator, and the outputs of the ON comparator and the OFF comparator are connected to the logic In the module Logic; Logic has five outputs, which respectively control the opening and closing of SW1~SW5.

The opening and closing sequence of each switch is that in the event detection stage, the switches SW1, SW2, SW4, and SW5 are in the open state, while SW3 is closed, and the amplifier A2 is used to amplify the light intensity change signal to determine whether the time is triggered; After generation, SW3, SW4 and SW5 maintain the original state, SW1 and SW2 are closed, and enter the event reset process; after the event reset process is completed, SW2 is opened, while SW3 is open and SW4 is closed, and enters the quantization stage. At this time, the amplifier A2 is used to convert Logarithmic photoresponse voltage output from the A1 feedback loop; the quantization phase lasts for several clock cycles to ensure full settling of the amplifier output signal. At the end of the quantization phase, SW5 is closed to read the output signal of the amplifier; after the quantization phase is over, SW4 and SW5 are disconnected, and SW2 and SW3 are closed, thus entering the quantization reset phase; when the quantization reset ends, SW1 and SW2 are disconnected , complete this event cycle, and enter the event detection process of the next event cycle.

Compared with prior art, technical characteristic and effect of the present invention:

1. The sensor using the amplifier multiplexing structure can not only monitor the change of the optical signal in real time, but also perform quantitative readout of the optical signal based on this structure.

2. The event detection process and quantitative readout process of the sensor use the same photodiode input signal, which avoids the signal deviation caused by the inconsistency of the light response and eliminates the detection-quantization error of the DVS pixel.

Description of drawings

Figure 1 Traditional DVS pixel structure diagram.

Figure 2 is a structure and timing diagram of a DVS pixel that uses amplifier multiplexing for quantitative readout of light intensity.

Detailed ways

On the basis of the traditional DVS structure, the present invention adds ports or components such as reference voltage, capacitor and switch, and increases the working process of two amplifiers, quantized readout and quantized reset, in one event cycle, so that the DVS structure itself has continuous optical power at the same time. Ability to monitor and quantify light intensity output.

The specific description is as follows:

The pixel structure adopted in the present invention and its working sequence are shown in FIG. 2 . The specific structure of the pixel is as follows: the photodiode PD is connected to the source stage of the logarithmic tube Mfb, and an amplifier A1 is added between the gate stage and the source stage of Mfb to form a negative feedback loop, which is used to convert the photocurrent detected by the photodiode to A switch SW3 is added between the capacitor C1 and the amplifier A2; one end of the switch SW4 is connected to the amplifier, and the other end is connected to the reference voltage Vref; C2 and the reset switch SW2 are respectively connected in parallel with the amplifier A2, and the capacitor C3 is connected in series with the switch SW1 in parallel. Connected to both ends of the amplifier A2; the output of A2 is connected to the ON comparator and the OFF comparator respectively, and the outputs of the two comparators are connected to the logic module Logic; Logic has five outputs, which respectively control the disconnection of SW1~SW5 open and close.

In the timing diagram, when SW1-SW5 are at low level, it means that the switch is open, and when it is at high level, it means that the switch is closed. In the event detection stage, the switches SW1, SW2, SW4 and SW5 are in the open state, and SW3 is closed. At this time, it is consistent with the event detection process in the traditional DVS. The amplifier A2 is used to amplify the light intensity change signal to determine whether the time is triggered. . After the event is generated, SW3, SW4 and SW5 maintain the original state, SW1 and SW2 are closed, and enter the event reset process. After the event reset process is completed, SW2 is opened, and at the same time, SW3 is opened and SW4 is closed to enter the quantization stage. At this time, the amplifier A2 is used to output the logarithmic light response voltage obtained by the A1 feedback loop. The quantization phase lasts several clock cycles to ensure complete settling of the amplifier output signal. At the end of the quantization phase SW5 is closed and the output signal of the amplifier is read out. After the quantization phase ends, SW4 and SW5 are disconnected, and SW2 and SW3 are closed, thereby entering the quantization reset phase. At the end of the quantization reset, SW1 and SW2 are disconnected, this event cycle is completed, and the event detection process of the next event cycle is entered.

Because the proposed method may have many implementations, here is an ideal solution.

An embodiment of the present invention is given by taking a 3.3V, 110nm manufacturing process as an example. A clock cycle of the designed image sensor is 20ns, and an event cycle is 160ns. Vref is 2.8V, C1 is 800fF, C2 is 50fF, C3 is 200fF, Vth, ON and Vth, OFF are both 40mV.

Claims (2)

1. one kind based on the multiplexing dynamic vision transducer of amplifier, it is characterized in that, electric diode PD is connected with the source class of logarithm pipe Mfb, and between the grid level and source class of Mfb, add amplifier A1 formation negative feedback loop, be converted to voltage in logarithmic fashion for the photoelectric current detected by photodiode; The grid level of logarithm pipe Mfb is also connected with electric capacity C1, adds interrupteur SW 3 between electric capacity C1 and amplifier A2; Interrupteur SW 4 one end connects amplifier A2 input, and the other end then connects reference voltage Vref; Electric capacity C2 and reset switch SW2 is in parallel with amplifier A2 respectively, and electric capacity C3 is attempted by the two ends of amplifier A2 after connecting with interrupteur SW 1; The output of A2 is connected with OFF comparator with ON comparator respectively, and the output of ON comparator and OFF comparator all accesses in logic module Logic; Logic has five outputs, and the disconnection of control SW1 ~ SW5 is with closed respectively.

2. as claimed in claim 1 based on the dynamic vision transducer that amplifier is multiplexing, it is characterized in that, each switch open and close sequential is, in the incident detection stage, interrupteur SW 1, SW2, SW4 and SW5 are in off-state, and SW3 closes, whether amplifier A2 is used for triggering being used for the time that judges after the amplification of light intensity variable signal; After event produces, SW3, SW4 and SW5 maintain the original state, SW1 and SW2 closes, and enters event resets process; After event resets process completes, SW2 disconnects, and the SW4 of SW3 disconnection simultaneously closes, and enters quantization stage, and the logarithm photoresponse voltage that now amplifier A2 is used for A1 feedback loop to obtain exports; Quantization stage continues some clock cycle, to ensure the foundation completely of amplifier output signal.At quantization stage end, SW5 closes, and reads the output signal of amplifier; After quantization stage terminates, SW4 and SW5 disconnects, SW2 and SW3 closes, thus enters into quantification reseting stage; At the end of quantizing to reset, SW1, SW2 disconnect, and complete the present event cycle, enter into the event detection process of next periods of events.