Front-end electronics for electromagnetic radiation sensor applications
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- AMS INTERNATIONAL AG
- Filing Date
- 2022-04-28
- Publication Date
- 2026-06-26
Smart Images
Figure CN117677867B_ABST
Abstract
Description
Technical Field
[0001] This disclosure relates to front-end electronic circuitry for electromagnetic radiation sensor applications, particularly X-ray imaging or photon counting applications such as multi-energy spectral CT (computed tomography). This disclosure also relates to photon counting sensor circuitry using front-end electronic circuitry, and to devices for medical diagnostics. Background Technology
[0002] Traditional CT scanners and X-ray imaging products use indirect conversion sensors. Indirect conversion sensors include a scintillator that converts X-rays into visible light, which is captured by a photodetector or photodiode to provide an electrical signal in response to the X-rays striking the scintillator material.
[0003] Unlike conventional computed tomography (CT) which uses indirect detection principles, direct conversion sensors allow the generation of electrical signals when incident photons strike direct conversion materials (such as CdTe / CZT). Direct conversion materials, along with continuous-time asynchronous front-end electronics, allow CT scanners to benefit from the advantages of photon counting systems. Photon counting medical imaging offers numerous advantages over conventional methods, such as better resolution and / or lower dose and spectral information.
[0004] Photon counting imaging systems require high-speed and asynchronous continuous-time processing of the input signal (input current pulse). Specifically, photon counting methods require a front-end circuit that receives the current input and provides a voltage at the output, which is shaped to facilitate further processing by a discriminator.
[0005] Front-end topologies are typically single-stage or two-stage. For small, fixed input capacitance, a single-stage architecture can be used, which incorporates a signal shaper circuit, including an amplifier circuit, followed by a discriminator and a counter.
[0006] Figure 1 A front-end electronic circuit 10 according to a single-stage scheme is shown, which includes a signal shaper circuit 1000 having an input terminal I10 to receive an input signal Iin from an electromagnetic radiation sensor (e.g., a photon detector). The signal shaper circuit 1000 includes an amplifier circuit 1100 having an input side that receives the input signal Iin from the sensor and a reference signal Vref, and an output side that provides an output signal Vout_shaper at an output terminal O10 of the front-end circuit. A capacitor 1300 is disposed in a feedback path 1002 between the input and output sides of the amplifier circuit 1100. A feedback element 1400, which can be configured as a resistor, is disposed in a feedback path 1001 connected in parallel with the capacitor 1300.
[0007] When an incident photon strikes the direct conversion material of the photon detector, a transient current signal is generated. This current is proportional to the energy of the incident photon. This current is applied as an input signal / input current pulse Iin to the input terminal I10 and is then processed by a signal shaper circuit 1000, which provides a shaped voltage at the output terminal O10. This shaped voltage is proportional to the input current, and therefore proportional to the energy of each individual incident photon. The shaper output voltage can be further processed by several discriminators and counters. The number of counts is proportional to the number of incident photons. Having multiple discriminators and counters will additionally provide energy level information for each incident photon.
[0008] For large and varying input capacitances, a two-stage architecture for the front-end electronics can be used. Instead of a single-stage signal shaper circuit, the two-stage front-end scheme includes a charge-sensitive amplifier coupled to the shaper amplifier, followed by a discriminator and a counter. Although the two-stage topology decouples the signal shaper stage from the input capacitance at the front-end electronics input, it introduces higher noise and power loss because the charge-sensitive amplifier acts as a buffer.
[0009] The baseline of the signal shaper circuit output is defined by a reference voltage connected to the positive input terminals of both the charge-sensitive amplifier and the shaper amplifier, which are typically differential-input and single-ended-output operational transconductance amplifiers (OTA).
[0010] The most important performance parameters of a photon counting front end are low power, low noise, high count rate, small FWHM (full width at half maximum) related to the pulse width of the shaped output, small silicon area, high linearity, and low ballistic defects.
[0011] To reduce the pulse width and thus the FWHM performance, and to increase the count rate, the aforementioned topology requires a significant power consumption. This introduces other problems, such as undesirable thermal and thermal stability effects in this system.
[0012] The most crucial building blocks of a photon counting front-end are the signal shaper circuit and its feedback element. The configuration of this module is critical to determining the performance of the front-end and, consequently, the overall system performance. To achieve the required bandwidth, the signal shaper circuit itself must exhibit a high transconductance (gm). However, to achieve sufficiently high bandwidth for a high count rate, the shaper circuit must consume a significant amount of power.
[0013] This is where the feedback elements come into play; they are the feedback resistor and the feedback capacitor. The feedback capacitor must be small enough to reduce FWHM for high count rates and to minimize stacking. However, a minimum capacitance is required to maintain sufficient phase margin and avoid stability issues.
[0014] Another feedback element is a resistor, which can be implemented using a standard resistor (e.g., a polysilicon resistor) operating in the linear region or a MOS transistor. The latter is preferred because it saves area, the resistance value can be very large, and it provides saturation behavior during pulsed activity when the shaper output is far from the baseline, as incident radiation impacts the target material of the sensor.
[0015] Another feedback implementation uses an active transconductor. However, this results in large input pulse amplitudes when there is a large input energy, or current starving when there is a stacking event, and thus the existing active feedback topology cannot process the input signal further.
[0016] There is a need for a solution for front-end electronic circuitry for electromagnetic radiation sensor applications that reduces pulse width, thereby reducing the FWHM of the shaper output, and additionally improves recovery from stacking without consuming excessive power in the signal shaper circuitry. Summary of the Invention
[0017] A front-end electronic circuit for electromagnetic radiation sensor applications enhances the pulse width, thereby enhancing the FWHM of the signal shaper output of the front-end electronic circuit and additionally improving the count rate during stacking.
[0018] The front-end electronic circuitry includes an input terminal configured to couple to an electromagnetic radiation sensor to receive an input signal from the sensor, and an output terminal providing an output signal. The front-end electronic circuitry includes a signal shaping circuit. The signal shaping circuitry includes an amplifier and an active dynamic feedback circuit disposed in the feedback path of the amplifier circuitry. The amplifier circuitry has an input node coupled to the input terminal of the front-end electronic circuitry, and an output node providing the output signal. The output node of the amplifier circuitry is coupled to the output terminal of the front-end electronic circuitry.
[0019] The active dynamic feedback circuit includes a first input transistor disposed in a first current path of the active dynamic feedback circuit. The active dynamic feedback circuit also includes a second input transistor disposed in a second current path of the active dynamic feedback circuit. The first input transistor has a control node for receiving an output signal. The second input transistor has a control node for receiving a reference signal. The active dynamic feedback circuit includes a buffer circuit configured to decouple the first current path and the second current path.
[0020] The proposed active dynamic feedback circuit allows for improvement in the input dynamic range of the signal shaper circuit and the current starving limit during accumulation events by enhancing the pulse shape and FWHM. To achieve this, the proposed active dynamic feedback circuit intentionally introduces nonlinearity by implementing a nonlinear feedback resistor (1 / gm) in the feedback path of the front-end electronics. As a result, the count rate is significantly improved without consuming excessive power in the signal shaper amplifier circuit. This topology is highly robust to PVT and mismatch. Furthermore, it allows the shaper output to be regulated to a reference signal voltage level independent of the PVT.
[0021] According to an embodiment of the front-end electronic circuit, the first current path and the second current path are respectively connected between the terminal providing the reference potential and the common node of the active dynamic feedback circuit. A buffer circuit is disposed between the common node and the first input transistor to decouple the first current path and the second current path.
[0022] The buffer circuit allows the bias currents of the first and second input transistors to be decoupled separately, so as to handle large signals or large deviations from the baseline at the shaper output without starving the second input transistor and causing clipping of the output.
[0023] According to an embodiment of the front-end electronic circuit, the active dynamic feedback circuit includes a third current path. The active dynamic feedback circuit also includes a current source disposed in the third current path between the terminal providing the power supply potential and the common node. The third current path is connected in series with each of the first and second current paths.
[0024] According to an embodiment of the front-end electronic circuit, the buffer circuit includes a first input node, a second input node, and an output node. The first input node of the buffer circuit is connected to a common node. The second input node of the buffer circuit is coupled to the output node of the buffer circuit. According to a possible embodiment, the second input node of the buffer circuit is directly connected to the output node of the buffer circuit; alternatively, according to another possible embodiment, the second input node of the buffer circuit is coupled to the output node of the buffer circuit via a feedback network. The output node of the buffer circuit is connected to the first input transistor.
[0025] According to an embodiment of the front-end electronic circuit, the buffer circuit includes a transistor and a current source. The transistor is disposed in the fourth current path of the active dynamic feedback circuit. The first and fourth current paths are connected in parallel between the terminal providing the reference potential and the second common node of the active dynamic feedback circuit. The current source is disposed in the fifth current path of the active dynamic feedback circuit, located between the terminal providing the power supply potential and the second common node. The current source coupled to the second common node ensures a stable current definition on the PVT.
[0026] According to an embodiment of the front-end electronic circuit, the buffer circuit includes an amplifier having a first input node connected to a common node of the active dynamic feedback circuit. The amplifier of the buffer circuit also includes a second input node connected to a second common node of the active dynamic feedback circuit. The amplifier of the buffer circuit has an output node connected to a control node of a transistor in the buffer circuit.
[0027] The amplifier in the buffer circuit allows the bias currents of the first input transistor and the transistor in the buffer circuit to be decoupled separately, so as to handle large signals or large deviations from the baseline at the shaper output without depleting the second input transistor and without causing clipping or saturation of the shaper output. Decoupling the first and fourth current paths through the buffer circuit enables the creation of a low-impedance node at the second common node of the active dynamic feedback circuit.
[0028] The decoupling of the corresponding bias currents in the first and fourth current paths allows for a small current in the first current path to achieve low transconductance and thus high resistance in the feedback path of the signal shaper circuit. On the other hand, the decoupling of the corresponding bias currents in the first and fourth current paths allows for a large current in the fourth current path to provide the excessive current required for the large signal generated at the output node of the amplifier circuit in the signal shaper circuit without becoming depleted and causing clipping of the output.
[0029] The amplifier in the buffer circuit provides impedance transformation, which allows the second common node of the active dynamic feedback circuit at the drain of the current source of the buffer circuit to be transformed from high impedance to low impedance.
[0030] According to an embodiment of the front-end electronic circuit, the first input transistor operates in the weak inversion region. As explained above, the active dynamic feedback circuit introduces nonlinearity by implementing a nonlinear feedback resistor. In contrast to, for example, MOS resistors typically provided in the feedback path of a signal shaper circuit, the nonlinearity is achieved specifically by biasing the first input transistor in the weak inversion region.
[0031] The MOS resistor in the feedback path of the signal shaper circuit needs to be biased in the strong inversion region to reduce resistance variations caused by its gate bias, which is extended by the PVT variation of the bias generator. Furthermore, nonlinearity is achieved by the fact that the potential of the second common node is fixed with a large current by the transistor in the buffer circuit of the fourth current path, thus making the second common node behave like a low-impedance node. The amplifier in the buffer circuit decouples the current in the first current path from the current in the fourth current path.
[0032] The nonlinearity intentionally introduced in the feedback path of the signal shaper stage by the active dynamic feedback circuit enables the full-amplitude signal of the output signal provided at the output node of the amplifier circuit of the signal shaper circuit to be overdriven to the first input transistor without being degraded by the voltage drop at the second common node of the buffer circuit that would otherwise occur.
[0033] According to an embodiment of the front-end electronic circuit, the first and second input transistors are matched to each other. Furthermore, the first current source of the active dynamic feedback circuit and the second current source of the buffer circuit can be matched to each other.
[0034] According to an embodiment of the front-end electronic circuit, the active dynamic feedback circuit includes a current mirror disposed between a first current path and a sixth current path of the active dynamic feedback circuit to couple current from the first current path into the sixth current path of the active dynamic feedback circuit. The sixth current path of the active dynamic feedback circuit is connected to the input node of the amplifier circuit of the signal shaper circuit.
[0035] The current mirror positioned between the first current path and the sixth current path of the active dynamic feedback circuit allows for small effective transconductance, i.e., high equivalent resistance, while utilizing a sufficiently high current to bias the first input transistor for speed and low offset.
[0036] According to an embodiment, the front-end electronic circuitry includes a reference signal generation circuit coupled to the control node of the second input transistor to provide a reference signal.
[0037] In addition to the active dynamic feedback circuit, the signal shaper circuit also includes a feedback capacitor positioned between the input and output nodes of the amplifier circuit. Furthermore, the signal shaper circuit includes a third current source positioned between the terminal providing the power supply potential and the input terminals of the front-end electronics. The first and third current sources are matched. The amplifier circuit can be implemented in a single-input single-output configuration or a differential-input single-output configuration.
[0038] Examples of possible applications of front-end electronic circuitry in a photon counting circuit.
[0039] The photon counting circuit includes front-end electronic circuitry according to one of the embodiments described above. The photon counting circuit also includes a photon detector having a photon-sensitive region. The photon detector is configured to generate a current pulse when a photon strikes the photon-sensitive region. The photon counting circuit also includes an energy discriminator connected to the output terminal of the front-end electronic circuitry.
[0040] A photon detector is connected to the input terminal of the front-end electronics circuit. The front-end electronics circuit is configured to generate a voltage pulse at its output node when a current pulse is applied to its input node. An energy discriminator is configured to generate a digital signal based on the level of the voltage pulse.
[0041] A device for medical diagnosis that uses the principle of photon counting.
[0042] As specified above, the device includes a photon counting circuit. The device can be configured as an X-ray device or a computed tomography scanner.
[0043] Additional features and advantages of the front-end electronic circuitry are set forth in the following detailed description. It should be understood that the foregoing general description and the following detailed description are merely exemplary and intended to provide an overview or framework for understanding the nature and characteristics of the claims. Attached Figure Description
[0044] The accompanying drawings are included to provide a further understanding and are incorporated in and form part of the specification. Thus, this disclosure will be more fully understood from the following detailed description, taken in conjunction with the accompanying drawings, in which:
[0045] Figure 1 A conventional embodiment of front-end electronic circuitry for electromagnetic radiation sensor applications is shown, including a differential signal shaper circuit with resistive feedback.
[0046] Figure 2A An embodiment of front-end electronic circuitry for electromagnetic radiation sensor applications is shown, including a differential input signal shaper circuit with active dynamic feedback circuitry.
[0047] Figure 2B An embodiment of a front-end electronic circuit for electromagnetic radiation sensor applications is shown, including a single-input signal shaper circuit with active dynamic feedback circuitry.
[0048] Figure 3A An embodiment of front-end electronic circuitry for electromagnetic radiation sensor applications is shown, including an active dynamic feedback circuit to improve input dynamic range and current depletion limitation during accumulation events by enhancing pulse shape;
[0049] Figure 3B A second embodiment of the front-end electronic circuitry for electromagnetic radiation sensor applications is shown, including an active dynamic feedback circuit that introduces nonlinearity by implementing a nonlinear feedback resistor.
[0050] Figure 4A A first embodiment of an active dynamic feedback circuit for the front-end electronics of an electromagnetic radiation sensor application with a folded auxiliary amplifier is shown.
[0051] Figure 4B A second embodiment of an active dynamic feedback circuit for the front-end electronics of an electromagnetic radiation sensor with a single-stage auxiliary amplifier is shown.
[0052] Figure 4C An embodiment of an active dynamic feedback circuit for the front-end electronics of an electromagnetic radiation sensor with a folded-cascode auxiliary amplifier is shown;
[0053] Figure 5A An architectural diagram of a first embodiment of a single-stage photon counting circuit with front-end electronics is shown;
[0054] Figure 5B A schematic diagram of a two-stage photon counting circuit with front-end electronics is shown; and
[0055] Figure 6 A device for medical diagnosis, including a photon counting circuit, is shown. Detailed Implementation
[0056] Figure 2A and Figure 2B Embodiments of a front-end electronic circuit 10 for electromagnetic radiation sensor applications are shown. The front-end electronic circuit 10 can be used as a photon count shaper in a photon counting circuit. The front-end electronic circuit 10 includes an input terminal I10 configured to couple to a sensor sensitive to electromagnetic radiation (e.g., X-ray radiation) to receive an input signal Iin from the sensor. The sensor can be configured as a photon detector. The front-end electronic circuit also includes an output terminal O10 to provide an output signal Vout_shaper.
[0057] The front-end electronic circuitry includes a signal shaper circuit 1000, which includes an amplifier circuit 1100 and an active dynamic feedback circuit 1200. The active dynamic feedback circuit 1200 is disposed in the feedback path 1001 of the front-end electronic circuitry 1000. The amplifier circuit 1100 has an input node I1100a coupled to the input terminal I10 of the front-end electronic circuitry, and an output node O1100 providing the output signal Vout_shaper. The output node O1100 of the amplifier circuit 1100 is coupled to the output terminal O10 of the front-end electronic circuitry 10. A feedback capacitor 1300 is disposed between the input node I1100a and the output node O1100 of the amplifier circuit 1100.
[0058] Figure 2A A differential input shaping scheme is illustrated, in which amplifier circuit 1100 is embodied in a differential input single output configuration. The differential input amplifier circuit 1100 has an input node I1100a that receives the input signal Iin, and a second input node I1100b that receives the reference signal Vref.
[0059] Figure 2B A single-input scheme for the front-end electronic circuit 10 is shown, wherein the amplifier circuit 1100 is embodied in a single-input single-output configuration. When compared with... Figure 2A Compared to the differential input shaping scheme shown, Figure 2B The amplifier circuit 1100 includes only a single input node I1100a to receive the input signal Iin. The amplifier circuit 1100 includes an input transistor 1110 having a control node coupled to the single input node I1100a. The amplifier circuit 1100 also includes a current source 1120 disposed in series with the input transistor 1110.
[0060] With Figure 1 Compared to the front-end electronic circuit shown, which includes resistive feedback, Figure 2A and Figure 2B The front-end electronic circuit 10 shown includes an active dynamic feedback circuit 1200 in the feedback path 1001 of the signal shaper circuit 1000. The active dynamic feedback circuit 1200 replaces... Figure 1 The feedback resistor of the signal shaper circuit in the front-end circuit.
[0061] The proposed active dynamic feedback circuit 1200 introduces nonlinearity by implementing a nonlinear feedback resistor (1 / gm). This scheme significantly reduces the pulse width, and thus the full width at half maximum (FWHM) of the shaper output, thereby improving the count rate during stacking. Furthermore, the front-end electronics 10 improves recovery from stacking. Consequently, the input dynamic range and count rate increase without consuming excessive power in the signal shaper circuitry.
[0062] Furthermore, the proposed active dynamic feedback circuit eliminates the need for a control loop within the high-speed path of the signal shaper circuit, thereby maximizing speed and phase margin. Additionally, the proposed active dynamic feedback circuit allows the use of a single-input amplifier circuit 1100, which can be configured as an operational transconductance amplifier, such as... Figure 2B As shown, this will further reduce power consumption and front-end noise. The proposed alternative is not used in feedback path 1001. Figure 1 The active dynamic feedback amplifier with 1400 resistors in the front-end circuit scheme and the single-input amplifier circuit of the signal shaper circuit are not feasible.
[0063] The active dynamic feedback circuit 1200 not only acts as a resistor via its transconductance gm, but also regulates the baseline at output node O1100 / output terminal O10 under the reference voltage Vref. Furthermore, the proposed active dynamic feedback circuit significantly improves the performance of the signal shaper circuit in terms of power consumption and FWHM.
[0064] Implementing an active dynamic feedback circuit in the feedback path 1001 of the signal shaper circuit 1000 with the requirements mentioned above is challenging. The reason behind these challenges is that such a circuit must meet the following requirements.
[0065] First, the active dynamic feedback circuit 1200 must be similar to a resistor. Assuming the active dynamic feedback circuit 1200 will be implemented as an operational transconductance amplifier comprising a pair of input transistors sharing the same tail node, this can be achieved using the resistance 1 / gm of one of the amplifier's input transistors. However, since the active dynamic feedback circuit 1200 must provide a very high resistance value, the transconductance gm of the input transistors must be very small, which can be achieved through a combination of small bias current and large overdrive voltage. The large overdrive voltage is typically limited by the supply voltage and the saturation of the current source coupled to the common tail node, while the small bias current affects the speed and the dynamic range that the active dynamic feedback circuit can operate in. A large dynamic range, i.e., handling large pulse or stacking events, will cause depletion of the other transistor in the input transistor pair sharing the same common-mode tail current.
[0066] Secondly, the active dynamic feedback circuit 1200 must improve the flow-through quality (FWHM). The active dynamic feedback circuit can improve the FWHM by reducing the pulse width during large-amplitude pulses or accumulation events. This occurs in nonlinear schemes, which significantly enhance the FWHM compared to using a resistor as the feedback element. However, to achieve this, the active dynamic feedback circuit must process the shaper output pulse very quickly and needs a high dynamic range within which it can effectively react to and reshape the output pulse. This necessitates a high transconductance gm, meaning a relatively large current at the input device. This contradicts the first requirement mentioned above, where a small current is needed to obtain a sufficiently large feedback resistor.
[0067] Third, the active dynamic feedback circuit 1200 must achieve low offset. The active dynamic feedback circuit is additionally responsible for tracking the reference voltage and adjusting the output baseline of the signal shaper circuit via feedback. Therefore, offset due to mismatch will cause a deviation from the baseline at the output node of the signal shaper circuit. A certain degree of deviation is acceptable because it can be corrected by the DAC at the comparator input. However, excessive deviation will shift the transconductance amplifier / comparator out of the input common-mode range, which is unacceptable.
[0068] Figure 3A An embodiment of a front-end electronics circuit 10 for electromagnetic sensor applications (e.g., for a photon counting front end) is shown, including a signal shaper circuit 1000 having an amplifier circuit 1100, an active dynamic feedback circuit 1200, and a feedback capacitor 1300. The signal shaper circuit 1000 includes a current source 1500 disposed between a terminal providing a power supply potential VDD and an input terminal I10 of the front-end electronics circuit 10. The front-end electronics circuit 10 allows for enhanced performance of the differential input amplifier circuit of the signal shaper circuit. Furthermore, the proposed embodiment of the front-end electronics circuit 10 enables the implementation of a single-input amplifier circuit for the signal shaper circuit.
[0069] refer to Figure 3AThe front-end electronic circuit 10 includes an active dynamic feedback circuit 1200, which includes a first input transistor 100 disposed in a first current path 1201 of the active dynamic feedback circuit. The active dynamic feedback circuit 1200 also includes a second input transistor 200 disposed in a second current path 1202 of the active dynamic feedback circuit 1200. The first input transistor 100 has a control node to receive an output signal Vout_shaper generated at the output node O1100 of the amplifier circuit 1100. The second input transistor 200 has a control node to receive a reference signal / voltage Vref. The active dynamic feedback circuit 1200 also includes a buffer circuit 300 configured to decouple the first current path 1201 and the second current path 1202.
[0070] The buffer circuit 300 thus allows the bias currents in the first current path and the second current path 1201, 1202 to be decoupled, which further allows large signals or large deviations from the baseline at the output node O1100 of the amplifier circuit 1100 of the signal shaper circuit 1000 to be processed without depleting the second input transistor 200 and without causing clipping of the output.
[0071] The first current path 1201 and the second current path 1202 are respectively connected between the terminal providing the reference potential VSS and the common node 1210 of the active dynamic feedback circuit 1200.
[0072] The active dynamic feedback circuit 1200 includes a third current path 1203. The active dynamic feedback circuit 1200 also includes a current source 400 disposed in the third current path 1203 between the terminal providing the power supply potential VDD and the common node 1210. The third current path 1203 is connected in series with each of the first current path 1201 and the second current path 1202.
[0073] A buffer circuit 300 is disposed between a common node 1210 and a first input transistor 100 to decouple the first current path 1201 from the second current path 1202. The buffer circuit 300 includes a first input node I300a, a second input node I300b, and an output node O300. The first input node I300a of the buffer circuit 300 is connected to the common node 1210. The second input node I300b of the buffer circuit 300 is coupled to the output node O300, meaning that the second input node I300b of the buffer circuit 300 can be directly connected to the output node O300, or it can be coupled to the output node O300 via a feedback network.
[0074] The active dynamic feedback circuit 1200 introduces nonlinearity. This is achieved in particular by the fact that the first input transistor 100 can operate in the weak inversion region, unlike a conventional MOS resistor that can be placed in the feedback path of a conventional signal shaper circuit. Conventional MOS resistors need to be biased in the strong inversion region to reduce the resistance variation caused by their Vgate bias, which is extended by the PVT variation of the bias generator.
[0075] The active dynamic feedback circuit 1200 may include a reference signal generation circuit 500 coupled to the control node of the second input transistor 200 to provide a reference signal / voltage Vref. The reference signal generation circuit 500 can correct the offset of the active dynamic feedback circuit. The reference signal generation circuit can be configured as a resistive DAC (digital-to-analog converter) to correct the offset of the active dynamic feedback circuit amplifier.
[0076] Figure 3B An advantageous embodiment with buffer circuit 300 is shown. Figure 3A The front-end electronic circuit 10.
[0077] The buffer circuit 300 includes a transistor 310 disposed in a fourth current path 1204 of the active dynamic feedback circuit 1200. The first current path 1201 and the fourth current path 1204 are connected in parallel between the terminal providing the reference potential VSS and the second common node 1220 of the active dynamic feedback circuit 1200. The buffer circuit 300 also includes a current source 320. The current source 320 is disposed in a fifth current path 1205 of the active dynamic feedback circuit 1200 between the terminal providing the power supply potential VDD and the second common node 1220.
[0078] According to an advantageous embodiment of the front-end electronic circuit 10, the first input transistor 100 and the second input transistor 200 are matched to each other. Furthermore, the current source 400 is matched to the current source 1500. Additionally, the current source 400 and the current source 320 are matched to each other.
[0079] The buffer circuit 300 also includes an (auxiliary) amplifier 330. The amplifier 330 has a first input node I330a connected to a common node 1210 of the active dynamic feedback circuit 1200. The amplifier 330 has a second input node I330b connected to a second common node 1220 of the active dynamic feedback circuit 1200, and an output node O330 connected to a control node of the transistor 310.
[0080] Decoupling of the bias current in the first current path 1201 and the bias current in the fourth current path 1204 allows for the creation of a low impedance at the second common node 1220. The (auxiliary) amplifier 330 provides impedance transformation. Specifically, the common tail node 1220 at the drain of the current source 320 can be transformed from high impedance to low impedance.
[0081] The nonlinearity is achieved by the fact that the potential of the common tail node 1220 can be fixed by the (auxiliary) amplifier 330 using a large current, making the common tail node 1220 behave like a low-impedance node. Decoupling of the input current in the first current path 1201 to the auxiliary current in the fourth current path 1204 is achieved via the (auxiliary) amplifier 330. Thus, the shaper output can be applied with its full signal amplitude to overdrive the first input transistor without being degraded by the voltage drop at the tail common node 1220 that would otherwise occur.
[0082] Finally, without the (auxiliary) amplifier, the negative input node I1100b of the active dynamic feedback circuit amplifier 1100 will deplete, and thus it will clip the output, especially in high-energy and / or stacking events. The decoupling of the positive and negative input bias currents allows for a small current in the positive input (i.e., a small current in the first current path 1201) to achieve low transconductance and thus high resistance in the feedback path 1001, and allows for a large current in the negative input (i.e., the fourth current path 1204) to provide the excess current required for the large signal at the shaper output without depleting and causing clipping of the output.
[0083] The main technical advantages of the front-end electronic circuit of the active dynamic feedback circuit 1200 included in the feedback path 1001 of the signal shaper circuit 1000 can be summarized as follows.
[0084] like Figure 3B As shown, an active dynamic feedback circuit 1200 provided in the feedback path 1001 of the signal shaper circuit 1000 allows for enhanced performance of the differential input shaper and makes the implementation of a single-input shaper feasible. The proposed active dynamic feedback circuit achieves a lower FWHM by enhancing (i.e. reducing) the pulse width, and thus operates at a higher count rate. This is achieved by intentionally introducing a highly nonlinear feedback resistor (1 / gm) between the input voltage and the output current, which is the opposite of the linear relationship in the case of polysilicon resistors or the quadratic relationship in the case of MOS resistors (NMOS) with the bulk and source connected to the shaper output.
[0085] The nonlinearity of the differential pair of the input transistors is increased by forcing its tail node 1220 to a constant voltage using an active feedback loop, causing the first input transistor 100 to experience a fully shaped output voltage as the gate-source voltage. Thus, a fully nonlinear relationship between the drain current of the (MOS) first input transistor 100 and the gate-source voltage is utilized.
[0086] By biasing in the weak inversion region, an exponential characteristic of the resistance in the feedback path can be achieved, thereby improving the FWHM. This improves the speed of the photon counting system and the count rate performance during stacking. Biasing in the weak inversion region is possible because overdriving of the first input transistor 100 can be decoupled from the shaper baseline by generating an appropriate reference voltage for the active feedback loop, i.e., the reference voltage Vref plus the gate-source voltage of the input transistor 200.
[0087] Simultaneously, for the standard differential transistor pair, the tail current source 320 ensures a stable current definition on the PVT. Since the active feedback loop defines the tail potential at the second common node 1220, it decouples the current in the fourth current path 1204 from the current in the first current path 1201. This allows for highly asymmetrical biasing of the first input transistor 100 and the transistor 310 of the buffer circuit 300 without the matching constraints that would otherwise occur in the standard differential pair.
[0088] According to the high feedback resistance requirement, the first input transistor 100 can be biased with a lower current, while the transistor 310 of the buffer circuit 300 can be biased with a large current, so as to achieve a low tail node impedance at the second common node 1220, and to complete tail potential clamping even at high frequencies where the active feedback loop is less efficient.
[0089] Because the active feedback loop and low tail node impedance maintain a constant tail node potential at the second common node 1220, independent of the shaper output, current depletion for large shaping peaks, as is possible in conventional differential pair schemes, is not possible. When the first input transistor 100 draws excess current in response to a large shaping peak, it will be provided by the asymmetric high-bias transistor 310 of the active feedback loop or buffer circuit 300. As a result, there is no current depletion for large shaping peaks because the transistor 310 of the active feedback loop and buffer circuit 300 can provide excess current in the first current path 1201.
[0090] Therefore, there are no limitations on stacking protection. Furthermore, there is no need to provide a transconductance controller to control the transconductivity of the active dynamic feedback circuit in the high-speed path, which allows the active dynamic feedback circuit 1200 to operate at high speed.
[0091] The active dynamic feedback circuit 1200 also includes a current mirror 600 disposed between the first current path 1201 and the sixth current path 1206 of the active dynamic feedback circuit 1200. The current mirror 600 includes a transistor 610 disposed in the first current path 1201 and a transistor 620 disposed in the sixth current path. The current mirror 600 is capable of coupling current from the first current path 1201 to the sixth current path 1206 of the active dynamic feedback circuit 1200. The sixth current path 1206 of the active dynamic feedback circuit 1200 is connected to the input node I1100a of the amplifier circuit 1100 of the signal shaper circuit 100. The gate nodes of transistors 610 and 620 may be connected via at least one resistor 630 to provide mirror pole compensation.
[0092] The current mirror 600 allows for reduction of the current in the first current path 1201. Therefore, reducing the current in the current path 1201 allows for a small effective transconductance while using a sufficiently high current to bias the first input transistor 100 for speed and low offset.
[0093] Figure 4A , Figure 4B and Figure 4C It shows Figure 3A and Figure 3B The diagram shows possible implementations of the active dynamic feedback circuit 1200. (Compared to...) Figure 3A and Figure 3B The same components in Figures 4A to 4C The same reference numerals are used to indicate them in the figures.
[0094] Figure 4A An implementation of an active dynamic feedback circuit 1200 for a folded auxiliary amplifier 330 with a buffer circuit 300 is shown. The auxiliary amplifier includes differential transistor pairs 331 and 332 coupled to a bias current source 333. The folded auxiliary amplifier 330 also includes a bias transistor 334, a cascode transistor 335, and a current mirror 336.
[0095] Figure 4B An implementation of an active dynamic feedback circuit 1200 is shown, which includes a folded cascode auxiliary amplifier 330 with a buffer circuit 300. The folded cascode auxiliary amplifier 330 includes differential transistor pairs 331 and 332, a bias current transistor 333, a bias transistor 334, a first cascode stage 335, a second cascode stage 337, and a current mirror 336.
[0096] Figure 4CA possible implementation of an active dynamic feedback circuit 1200 with a single-stage auxiliary amplifier 330 having a buffer circuit 300 is shown. The auxiliary amplifier 330 includes differential transistor pairs 331 and 332, a bias transistor 333, and a current mirror 338.
[0097] The proposed front-end electronic circuit 10 design includes a signal shaper circuit 1000, which has an active dynamic feedback circuit 1200 in the feedback path 1001, and can be used in situations such as... Figure 5A The single-level architecture shown or as Figure 5B The photon counting circuit is provided in the two-level architecture scheme shown. Figure 5A and Figure 5B An active dynamic feedback circuit 1200 in a differential input configuration is shown. It is also possible to implement the active dynamic feedback circuit 1200 in a single-input configuration.
[0098] refer to Figure 5A The photon counting circuit 2 has a single-stage architecture, with a photon detector 20 having a photon-sensitive region 21 connected to the input terminal I10 of the front-end electronic circuit 10. The photon detector 20 is configured to generate a current pulse when a photon strikes the photon-sensitive region 21.
[0099] Front-end electronics 10 is configured to generate a voltage pulse for the output signal Vout_shaper at output node O10 when a current pulse generated by photon detector 20 is applied to input terminal I10 of front-end electronics 10. The shaper output voltage Vout_shaper is then further processed by several discriminator circuits 30a, ..., 30n of energy discriminator 30. Energy discriminator 30 is configured to generate a digital signal based on the level of the voltage pulse at output terminal O10. The output of the discriminator is then fed into counter circuits 40a, ..., 40n of counter 40. The number of counts is proportional to the number of incident photons. Having multiple discriminator circuits 30a, ..., 30n and counter circuits 40a, ..., 40n will provide information about the energy level of each incident photon. The counter output can be... Figure 5A DSP (Digital Signal Processor) processing, not shown.
[0100] For small and fixed input capacitors, the following can be used: Figure 5A The single-stage architecture of photon counting circuit 2 is shown. For large and varying input capacitances, a method such as... Figure 5B The two-stage architecture scheme of the photon counting circuit 2 shown is illustrated.
[0101] refer to Figure 5BThe photon counting circuit 2 has a two-stage architecture. The signal shaper circuit 1000 is coupled to the input terminal I10 via a charge-sensitive amplifier circuit 2000, which acts as a buffer to decouple the signal shaper circuit 1000 from the input capacitor at the input terminal I10. The charge-sensitive amplifier circuit 2000 includes an operational transconductance amplifier 2100, a feedback resistor 2200, and a feedback capacitor 2300. The charge-sensitive amplifier circuit 2000 and the signal shaper circuit 1000 are coupled via a coupling network 3000, which includes a parallel connection of a resistor 3100 and a capacitor 3200.
[0102] When an active dynamic feedback circuit 1200 is used in the signal shaper circuit of the front-end electronics in photon counting applications, a small FWHM can be achieved, which provides a budget in terms of speed and count rate to increase the capacitance of the feedback capacitor 1300. By increasing the capacitance of capacitor 1300, a low ballistic defect can be achieved.
[0103] In addition to using front-end electronic circuitry 10 in photon counting applications, the proposed circuitry includes, for example... Figure 3A , Figure 3B or Figures 4A to 4C The configuration of the front-end electronic circuit 10 of the active dynamic feedback circuit 1200 shown can be used for various X-ray imaging applications, such as computed tomography, security, food or baggage inspection, material and electronic product defect inspection, etc.
[0104] Figure 6 An example of an application is shown, wherein a photon counting circuit 2 is provided in a device 1 for medical diagnosis, the photon counting circuit 2 being equipped with according to Figure 3A , Figure 3B or Figures 4A to 4C One of the illustrated solutions includes a front-end electronic circuit 10. The device 1 for medical diagnosis can be configured as, for example, an X-ray machine or a computed tomography scanner.
[0105] To familiarize the reader with novel aspects of front-end circuit design, embodiments of the front-end electronic circuits disclosed herein have been discussed. Although preferred embodiments have been shown and described, those skilled in the art can make many changes, modifications, equivalents, and substitutions to the disclosed concepts without unnecessarily departing from the scope of the claims.
[0106] Specifically, the design of the front-end electronic circuitry is not limited to the disclosed embodiments, and examples of as many alternatives as possible to the features included in the discussed embodiments are given. However, any modifications, equivalents, and substitutions of the disclosed concepts are intended to be included within the scope of the appended claims.
[0107] Features recited in individual dependent claims can be advantageously combined. Furthermore, the reference numerals used in the claims are not intended to limit the scope of the claims.
[0108] Furthermore, as used herein, the term "comprising" does not exclude other elements. Additionally, as used herein, the article "a" is intended to include one or more components or elements, and is not limited to being interpreted as meaning only one.
[0109] This patent application claims priority to German patent application No. 102021111362.8, the disclosure of which is incorporated herein by reference.
[0110] List of reference numerals
[0111] 1. Equipment used for medical diagnosis
[0112] 2. Photon counting circuit
[0113] 10. Front-end electronic circuits
[0114] 20 photon detectors
[0115] 30 Energy Discriminator
[0116] 40 counter
[0117] 100 First Input Transistor
[0118] 200 Second Input Transistor
[0119] 300 buffer circuit
[0120] 310 transistors
[0121] 320 Current Source
[0122] 330 amplifier
[0123] 400 Current Source
[0124] 500 Reference Signal Generation Circuit
[0125] 600 Current Mirror
[0126] 1000 signal shaper circuit
[0127] 1100 Amplifier Circuit
[0128] 1200 Active Dynamic Feedback Circuit
[0129] 1300 capacitor
[0130] 2000 Charge-Sensitive Amplifier Circuit
[0131] 2100 Operational Transconductance Amplifier
[0132] 2200 feedback resistor
[0133] 2300 capacitor
[0134] 3000 Coupled Network
[0135] 3100 capacitor
[0136] 3200 resistor
Claims
1. A front-end electronic circuit for electromagnetic radiation sensor applications, comprising: - Input terminal (I10), which is configured to be coupled to an electromagnetic radiation sensor to receive an input signal (Iin) from the sensor. - Output terminal (O10) provides the output signal (Vout_shaper). - A signal shaper circuit (1000) includes an amplifier circuit (1100) and an active dynamic feedback circuit (1200), wherein the active dynamic feedback circuit (1200) is disposed in the feedback path (1001) of the signal shaper circuit (1000). - The amplifier circuit (1100) has an input node (I1100a) coupled to the input terminal (I10) and an output node (O1100) that provides the output signal (Vout_shaper), the output node (O1100) being coupled to the output terminal (O10). - The active dynamic feedback circuit (1200) includes a first input transistor (100) disposed in a first current path (1201) of the active dynamic feedback circuit, and a second input transistor (200) disposed in a second current path (1202) of the active dynamic feedback circuit (1200). - Wherein, the first input transistor (100) has a control node that receives the output signal (Vout_shaper), - Wherein, the second input transistor (200) has a control node for receiving a reference signal (Vref), - The active dynamic feedback circuit (1200) includes a buffer circuit (300) configured to decouple the first current path and the second current path (1201, 1202).
2. The front-end electronic circuit according to claim 1, - Wherein, the first current path (1201) and the second current path (1202) are respectively connected between the terminal providing the reference potential (VSS) and the common node (1210) of the active dynamic feedback circuit (1200). - in, The buffer circuit (300) is disposed between the common node (1210) and the first input transistor (100).
3. The front-end electronic circuit according to claim 2, - The active dynamic feedback circuit (1200) includes a third current path (1203). - in, The active dynamic feedback circuit (1200) includes a current source (400) disposed in the third current path (1203) between the terminal providing the power supply potential (VDD) and the common node (1210). - Wherein, the third current path (1203) is connected in series to each of the first current path and the second current path (1201, 1202).
4. The front-end electronic circuit according to claim 3, - in, The buffer circuit (300) includes a first input node, a second input node (I300a, I300b), and an output node (O300). - Wherein, the first input node (I300a) of the buffer circuit (300) is connected to the common node (1210). - Wherein, the second input node (I300b) of the buffer circuit (300) is coupled to the output node (O300) of the buffer circuit (300). - Wherein, the output node (O300) of the buffer circuit (300) is connected to the first input transistor (100).
5. The front-end electronic circuit according to claim 3 or 4, - in, The buffer circuit (300) includes a transistor (310) and a current source (320). - Wherein, the transistor (310) is disposed in the fourth current path (1204) of the active dynamic feedback circuit (1200), - Wherein, the first current path (1201) and the fourth current path (1204) are connected in parallel between the terminal providing the reference potential (VSS) and the second common node (1220) of the active dynamic feedback circuit (1200). - Wherein, the current source (320) is disposed in the fifth current path (1205) of the active dynamic feedback circuit (1200) between the terminal providing the power supply potential (VDD) and the second common node (1220).
6. The front-end electronic circuit according to claim 5, in, The buffer circuit (300) includes an amplifier (330) having a first input node (I330a) connected to the common node (1210) of the active dynamic feedback circuit (1200), a second input node (I330b) connected to the second common node (1220) of the active dynamic feedback circuit (1200), and an output node (O330) connected to the control node of the transistor (310).
7. The front-end electronic circuit according to claim 1, comprising: A reference signal generation circuit (500) coupled to the control node of the second input transistor (200) provides the reference signal (Vref).
8. The front-end electronic circuit according to claim 1, - The active dynamic feedback circuit (1200) includes a current mirror (600) disposed between the first current path (1201) and the sixth current path (1206) of the active dynamic feedback circuit (1200) to couple current from the first current path (1201) into the sixth current path (1206) of the active dynamic feedback circuit (1200). - in, The sixth current path (1206) of the active dynamic feedback circuit (1200) is connected to the input node (1100a) of the amplifier circuit (1100) of the signal shaper circuit (1000).
9. The front-end electronic circuit according to claim 8, - The current mirror (600) includes a first mirror transistor (610) disposed in the first current path (1201) and a second mirror transistor (620) disposed in the sixth current path (1206). - in, The current mirror (600) includes at least one resistor (630) disposed between the gate node of the first mirror transistor (610) and the gate node of the second mirror transistor (620).
10. The front-end electronic circuit according to claim 1, in, The first input transistor (100) operates in the weak inversion region.
11. The front-end electronic circuit according to claim 1, - in, The first input transistor and the second input transistor (100, 200) are matched to each other, and / or - Wherein, the first current source (400) and the second current source (320) are matched with each other.
12. The front-end electronic circuit according to claim 1, - Wherein, the signal shaper circuit (1000) includes a feedback capacitor (1300) disposed between the input node (I1100a) and the output node (O1100) of the amplifier circuit (1100). - in, The signal shaper circuit (1000) includes a third current source (1500) disposed between the terminal providing the power supply potential (VDD) and the input terminal (I10). - Wherein, the first current source (400) is matched with the third current source (1500).
13. The front-end electronic circuit according to claim 1, in, The amplifier circuit (1100) is embodied in a single-input single-output configuration or a differential-input single-output configuration.
14. A photon counting circuit, comprising: The front-end electronic circuit (10) according to claim 1. - A photon detector (20) having a photon-sensitive region (21), the photon detector (20) being configured to generate a current pulse when a photon strikes the photon-sensitive region (21), - Energy discriminator (30) connected to the output terminal (O10) of the front-end electronic circuit (10). - Wherein, the photon detector (20) is connected to the input terminal (I10) of the front-end electronic circuit (10). - Wherein, the front-end electronic circuit (10) is configured to generate a voltage pulse at the output terminal (O10) of the front-end electronic circuit (10) when the current pulse is applied to the input terminal (I10) of the front-end electronic circuit (10). - Wherein, the energy discriminator (30) is configured to generate a digital signal based on the level of the voltage pulse.
15. A device for medical diagnosis, comprising: - Photon counting circuit (2) according to claim 14. - Wherein, the device (1) is configured as an X-ray device or a computed tomography scanner.