Transimpedance amplification circuits and measuring instruments

Abstract

To provide a transimpedance amplifier circuit capable of amplifying current with low noise and high magnification, and a measuring instrument equipped therewith. [Solution] A transimpedance amplification circuit comprising: a first transimpedance amplifier that converts current to voltage; and at least one circuit block connected downstream of the first transimpedance amplifier, wherein each circuit block includes a conversion circuit that converts voltage to current, and a second transimpedance amplifier connected downstream of the conversion circuit that converts current to voltage. A measuring instrument comprising the transimpedance amplification circuit.

Description

Technical Field

[0001] The present disclosure relates to a transimpedance amplifier circuit and a measuring instrument.

Background Art

[0002] Conventionally, a technique for realizing a broadband and high-gain transimpedance amplifier by providing a feedback circuit is known (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In order to achieve high sensitivity in measurement in a measuring instrument such as an optical measuring instrument or a radiation measuring instrument, it is required to amplify a minute current with low noise and high magnification. An RGC (regulated Cascode) circuit, which is one of transimpedance amplifiers, can amplify a current with lower noise and higher magnification than other methods.

[0005] In amplification by a single-stage RGC circuit, there is a limit to increasing the magnification. Therefore, in the conventional technology, a voltage amplifier circuit is connected to the subsequent stage of a single-stage RGC circuit. However, in the voltage amplification method, it is difficult to reduce noise due to thermal noise of transistors or resistors. Therefore, in a conventional transimpedance amplifier circuit in which a voltage amplifier circuit is connected to the subsequent stage of a single-stage RGC circuit, it is difficult to reduce noise in the entire circuit.

[0006] The present disclosure provides a transimpedance amplifier circuit capable of amplifying a current with low noise and high magnification, and a measuring instrument including the same.

Means for Solving the Problems

[0007] As one aspect of this disclosure, A first transimpedance amplifier that converts current into voltage, The system comprises at least one circuit block connected to the subsequent stage of the first transimpedance amplifier, Each of the aforementioned circuit blocks is: A conversion circuit that converts voltage to current, A transimpedance amplification circuit is provided, which includes a second transimpedance amplifier that converts current to voltage and is connected downstream of the aforementioned conversion circuit.

[0008] Another aspect of this disclosure is, A measuring instrument equipped with the said transimpedance amplification circuit is provided. [Effects of the Invention]

[0009] According to this disclosure, a transimpedance amplifier circuit capable of amplifying current with low noise and high magnification, and a measuring instrument equipped therewith, can be provided. [Brief explanation of the drawing]

[0010] [Figure 1] This figure shows an example configuration of a measuring instrument equipped with a transimpedance amplification circuit according to the first embodiment. [Figure 2] This is a circuit diagram showing a specific example of a measuring instrument equipped with a transimpedance amplification circuit according to the first embodiment. [Figure 3] This figure shows an example configuration of a measuring instrument equipped with a transimpedance amplification circuit according to the second embodiment. [Figure 4] This is a circuit diagram showing a specific example of a measuring instrument equipped with a transimpedance amplification circuit according to the second embodiment. [Figure 5] This is a circuit diagram showing a specific example of a common-emitter transimpedance amplifier. [Figure 6] This is a circuit diagram showing a specific example of a common-base transimpedance amplifier. [Figure 7] This is a circuit diagram showing a specific example of a V / I conversion circuit using a PNP transistor. [Figure 8] This is a circuit diagram showing a specific example of a V / I conversion circuit using an NPN transistor. [Figure 9] This is a circuit diagram showing a specific example of a V / I conversion circuit of the current mirror type. [Figure 10] This is a circuit diagram showing a specific example of a V / I conversion circuit of the multi-current mirror type.

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0012] The present disclosure provides a means for realizing high sensitivity of a transimpedance amplifier circuit, which is one of the photocurrent-electricity conversion amplifiers used in measuring instruments such as optical measuring instruments or radiation measurements. This means is particularly suitable for use in the front-end amplification of portable radiation measuring instruments that require operation with low power consumption.

[0013] <S FIG. 1 is a diagram showing a configuration example of a measuring instrument including a transimpedance amplifier circuit according to the first embodiment. The measuring instrument 201 includes a radiation sensor 1, a transimpedance amplifier circuit 101, and a detection circuit 4.

[0014] The radiation sensor 1 is an example of a sensor that outputs current or charge to the first-stage I / V transimpedance amplifier 10 in the transimpedance amplifier circuit 101 via AC coupling (alternating current coupling). The radiation sensor 1 may be reversely biased for high sensitivity and wide bandwidth. In order to remove the reverse bias voltage, the output of the radiation sensor 1 is input to the first-stage I / V transimpedance amplifier 10 in the transimpedance amplifier circuit 101 via AC coupling.

[0015] The transimpedance amplifier circuit 101 is a converter that converts current to voltage. In this example, the transimpedance amplifier circuit 101 converts a current pulse corresponding to the amount of charge output from the radiation sensor 1 into a voltage pulse, and outputs the converted voltage pulse to the level comparator 2 in the detection circuit 4. The transimpedance amplifier circuit 101 generates a voltage pulse with a peak value proportional to the amount of charge output from the radiation sensor 1.

[0016] The detection circuit 4 detects the energy of radiation (e.g., alpha rays) based on voltage pulses from the transimpedance amplifier circuit 101. For example, the detection circuit 4 generates an energy spectrum as a histogram of the number of voltage pulses that fall within a reference energy width within a reference time. From the generated energy spectrum, the detection circuit 4 can calculate the radioactive nuclides contained in the sample and their concentrations. The detection circuit 4 outputs the detection results based on the voltage pulses from the transimpedance amplifier circuit 101 to the outside.

[0017] The detection circuit 4 includes, for example, a level comparator 2 and a counter 3.

[0018] Level comparator 2 is an example of a comparator to which the output of the I / V transimpedance amplifier 20, which is included in the last stage circuit block of at least one of the circuit blocks 50 in the transimpedance amplification circuit 101, is input. Level comparator 2 compares the voltage pulse from the I / V transimpedance amplifier 20 included in the last stage circuit block 50 with a predetermined threshold voltage and outputs a pulse voltage signal representing the result of the comparison.

[0019] Counter 3 counts pulse voltage signals from level comparator 2. Detection circuit 4 can calculate the radioactive nuclides and their concentrations contained in the sample based on the number of pulse voltage signals counted by counter 3.

[0020] The transimpedance amplifier circuit 101 comprises an I / V transimpedance amplifier 10 that converts current to voltage, and at least one circuit block 50 that is cascaded after the I / V transimpedance amplifier 10. Figure 1 illustrates a configuration in which three circuit blocks 50 are cascaded after the I / V transimpedance amplifier 10. The number of circuit blocks 50 is not limited to three; at least one is sufficient.

[0021] The I / V transimpedance amplifier 10 is an example of a first transimpedance amplifier that converts current to voltage. Each of the M circuit blocks 50 includes a V / I conversion circuit 30 that converts voltage to current, and an I / V transimpedance amplifier 20 that is cascaded after the V / I conversion circuit 30. M is an integer of 1 or more. The I / V transimpedance amplifier 20 is an example of a second transimpedance amplifier that converts current to voltage.

[0022] Examples of I / V transimpedance amplifiers include the RGC circuit shown above, a common-emitter transimpedance amplifier (Figure 5), and a common-base transimpedance amplifier (Figure 6). By employing these example circuits as I / V transimpedance amplifiers 10 and 20, current can be amplified with low power consumption, low noise, and high magnification.

[0023] In Figures 5 and 6, I in This represents the current output from radiation sensor 1. PD This represents the input capacitance, such as the parasitic capacitance of radiation sensor 1. The common-emitter transimpedance amplifier in Figure 5 consists of transistor Q1 and resistor R. C and resistor R F The common-base transimpedance amplifier in Figure 6 has transistor Q1 and resistor R C and resistor R E It has.

[0024] In this disclosure, in order to increase the amplification factor of the transimpedance amplifier circuit 101, the transimpedance amplifier circuit 101 comprises N I / V transimpedance amplifiers, where N is an integer greater than or equal to 2. The N I / V transimpedance amplifiers include the first-stage I / V transimpedance amplifier 10 and M I / V transimpedance amplifiers 20 (N = M + 1).

[0025] Since the output of an I / V transimpedance amplifier is a voltage output, it is not possible to directly connect another I / V transimpedance amplifier after it. Therefore, a V / I conversion circuit 30 is provided between the preceding I / V transimpedance amplifier and the subsequent I / V transimpedance amplifier. The gain of the V / I conversion circuit 30 should preferably be relatively low to avoid generating noise.

[0026] Examples of V / I conversion circuits include an emitter follower (or source follower) with a gain of 1, a V / I conversion circuit that converts voltage to current using a PNP transistor (Figure 7), a V / I conversion circuit that converts voltage to current using an NPN transistor (Figure 8), a V / I conversion circuit that converts voltage to current using a current mirror circuit (Figure 9), and a V / I conversion circuit that converts voltage to current using a multicurrent mirror circuit (Figure 10). The V / I conversion circuit may also be a circuit that converts voltage to current using a J-FET or an operational amplifier. By adopting one of these example circuits as the V / I conversion circuit 30, the gain of the V / I conversion circuit 30 can be reduced, making it possible to reduce noise.

[0027] The V / I conversion circuit in Figure 7 converts a positive voltage Vi into a current Iout using a PNP transistor TR1. The V / I circuit in Figure 7 has a PNP transistor TR1 and a resistor R. The PNP transistor TR1 has a base that is grounded, an emitter that is connected to the voltage Vi via the resistor R, and a collector that outputs a current Iout.

[0028] The V / I conversion circuit in Figure 8 converts a negative voltage Vi to a current Iout using an NPN transistor TR1. The V / I circuit in Figure 8 has an NPN transistor TR1 and a resistor R. The NPN transistor TR1 has a base that is grounded, an emitter that is connected to the voltage Vi via the resistor R, and a collector that outputs a current Iout.

[0029] The V / I conversion circuit in Figure 9 converts voltage Vi to current Iout using a current mirror circuit 31. The V / I conversion circuit in Figure 9 includes a current mirror circuit 31, resistors R9 and R10, and transistor Q6. The current mirror circuit 31 is a current mirror circuit using transistors Q4 and Q5.

[0030] The V / I conversion circuit in Figure 10 converts voltage Vi to current Iout using a current mirror circuit 32. The V / I conversion circuit in Figure 10 includes a current mirror circuit 32, resistors R9 and R10, and transistor Q6. The current mirror circuit 32 is a multi-current mirror circuit using transistors Q4, Q5, Q8, and Q9.

[0031] As described above, the transimpedance amplifier circuit 101 shown in Figure 1 comprises a transimpedance amplifier 10 that converts current to voltage, and at least one circuit block 50 connected downstream of the transimpedance amplifier 10. Each of the at least one circuit block 50 includes a V / I conversion circuit 30 that converts voltage to current, and an I / V transimpedance amplifier 20 connected downstream of the V / I conversion circuit 30 that converts current to voltage. The N I / V transimpedance amplifiers, consisting of the first-stage I / V transimpedance amplifier 10 and the M I / V transimpedance amplifiers 20, improve the amplification factor of the transimpedance amplifier circuit 101. Furthermore, since the low-gain V / I conversion circuit 30 is connected between the preceding I / V transimpedance amplifier and the subsequent I / V transimpedance amplifier, the increase in noise is suppressed. Therefore, the configuration shown in Figure 1 provides a transimpedance amplifier circuit 101 capable of amplifying current with low noise and high magnification, and a measuring instrument 201 equipped therewith.

[0032] Figure 2 is a circuit diagram showing a specific example of a measuring instrument equipped with a transimpedance amplifier circuit according to the first embodiment. Figure 2 shows the case where there is one circuit block 50. The measuring instrument 201 includes a radiation sensor 1, a reverse bias circuit 40, a DC cut circuit 70, a transimpedance amplifier circuit 101, and a detection circuit 4.

[0033] The radiation sensor 1 has a radiation detection element D1. The radiation detection element D1 may be formed by creating a pn junction or heterojunction on one side of a high-resistivity single-crystal silicon wafer, and applying a reverse bias to this junction to form depletion layers on both sides of the junction. The radiation detection element D1 outputs a charge in accordance with the energy of the radiation (e.g., gamma rays) incident on the depletion layer.

[0034] The reverse bias circuit 40 applies a reverse bias V1 to the radiation detection element D1. The reverse bias circuit 40 includes resistors R12, R5, R4 and capacitors C8, C2.

[0035] The DC cut circuit 70 cuts the DC component input to the I / V transimpedance amplifier 10. In this example, the DC cut circuit 70 has a capacitor C1 connected between the radiation sensor 1 and the I / V transimpedance amplifier 10, and the DC component input to the I / V transimpedance amplifier 10 is cut by the capacitor C1. The capacitor C1 AC couples the radiation sensor 1 and the I / V transimpedance amplifier 10.

[0036] The I / V transimpedance amplifier 10 is an RGC type transimpedance amplifier. The I / V transimpedance amplifier 10 has transistors Q1 and Q7, resistors R1, R2, R3, and capacitors C6 and C7. Transistor Q1 has a base connected to node N1, a base connected to ground GND, and a collector connected to node N2. Node N1 is the connection point between the emitter of transistor Q7 and one end of resistor R3, and the cathode of radiation detection element D1 is connected via capacitor C1. Resistor R3 is connected between node N1 and ground GND. Transistor Q7 has a base connected to node N2, an emitter connected to node N1, and a collector connected to node N3. Resistor R1 is connected between the power supply voltage V2 and node N3. Capacitor C6 is connected in parallel with resistor R1. Resistor R2 is connected between the power supply voltage V2 and node N2. Capacitor C7 is connected in parallel with resistor R2.

[0037] The V / I conversion circuit 30 is an emitter follower that converts the voltage output from node N3 of the I / V transimpedance amplifier 10 into a current and outputs it. The V / I conversion circuit 30 has a transistor Q4, a resistor R9, and a capacitor C3. Transistor Q4 has a base connected to node N3, a collector connected to the power supply voltage V2, and an emitter connected to ground GND via resistor R9. Capacitor C3 cuts the DC component input to the I / V transimpedance amplifier 20.

[0038] The I / V transimpedance amplifier 20 is an RGC type transimpedance amplifier and has the same circuit configuration as the I / V transimpedance amplifier 10. The I / V transimpedance amplifier 20 has transistors Q2 and Q3, resistors R7, R6, and R8, and capacitors C4 and C5. Nodes N11, N12, and N13 correspond to nodes N1, N2, and N3. Capacitor C10 cuts the DC component input to the level comparator 2.

[0039] The level comparator 2 includes a voltage divider circuit that divides the voltage from the I / V transimpedance amplifier 20 using resistors R13 and R14, a comparator U1 that compares the output voltage of the voltage divider circuit with a reference voltage REF, and resistors R15 and R16 connected to the comparator U1.

[0040] The RGC-type I / V transimpedance amplifiers 10 and 20 are low-power, high-speed, and low-noise, and the V / I conversion circuit 30 is an emitter follower with a gain of 1. Therefore, even with a high gain, the transimpedance amplification circuit 101 can achieve reduced power consumption and reduced noise.

[0041] Figure 3 shows an example configuration of a measuring instrument equipped with a transimpedance amplifier circuit according to the second embodiment. In the second embodiment, a description of the configuration, operation, and effects similar to those of the first embodiment will be omitted by referring to the above description.

[0042] The transimpedance amplifier circuit 102 shown in Figure 3 includes a feedback circuit 60 that feeds back at least one output of M circuit blocks 50. The feedback circuit 60 achieves high-frequency amplification and stabilization of the transimpedance amplifier circuit 102 by feeding back at least one output of M circuit blocks 50.

[0043] The feedback circuit 60 feeds back at least one output of the M I / V transimpedance amplifiers 20. For example, the feedback circuit 60 feeds back at least one output of the M I / V transimpedance amplifiers 20 to the stage before the I / V transimpedance amplifier 10. This enables higher frequency amplification and stabilization of the transimpedance amplification circuit 102. The stage before the I / V transimpedance amplifier 10 is not limited to the input of the I / V transimpedance amplifier 10, but may be a circuit before the input of the I / V transimpedance amplifier 10. A circuit before the input of the I / V transimpedance amplifier 10 is, for example, the circuit between the radiation sensor 1 and the input of the I / V transimpedance amplifier 10.

[0044] The feedback circuit 60 may feed back the output of the I / V transimpedance amplifier 20 to part or all of the input of the I / V transimpedance amplifier 20 and the input of at least one or more I / V transimpedance amplifiers 20 located upstream of the I / V transimpedance amplifier 20. This enables higher frequency amplification and stabilization of the transimpedance amplification circuit 102.

[0045] Figure 4 is a circuit diagram showing a specific example of a measuring instrument equipped with a transimpedance amplifier circuit according to the second embodiment. The transimpedance amplifier circuit 102 shown in Figure 4 differs from the transimpedance amplifier circuit 101 shown in Figure 2 in that it includes a feedback circuit 60.

[0046] In Figure 4, the feedback circuit 60 feeds back the output of the I / V transimpedance amplifier 20 to node N1, which is the input to the I / V transimpedance amplifier 10, via resistors R10 and R11. The feedback circuit 60 further feeds back the output of the I / V transimpedance amplifier 20 to its input via resistor R11. The series circuit of resistors R10 and R11 is connected between node N13 and node N1. The intermediate node between resistors R10 and R11 is connected between the output of the V / I conversion circuit 30 (emitter of transistor Q4) and the input of the I / V transimpedance amplifier 20 (node ​​N11). More specifically, this intermediate node is connected between the emitter of transistor Q4 and capacitor C3.

[0047] The present invention is not limited by the embodiments described above. The embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, and modifications are possible without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents.

[0048] For example, the sensor that outputs current or charge to the input of the transimpedance amplifier 10 via AC coupling is not limited to the radiation sensor 1, but may be other sensors such as a light sensor that detects light.

[0049] The transistor is not limited to bipolar transistors; MOS transistors can also be used. In this case, the base should be read as the gate, the collector as the drain, and the emitter as the source. [Explanation of symbols]

[0050] 1. Radiation sensor 2-level comparator 3 counters 4. Detection circuit 10,20 I / V Transimpedance Amplifier 30 V / I conversion circuit 40 Reverse bias circuit 50 Circuit Blocks 60 Feedback Circuit 70 DC cut-off circuit 101,102 Transimpedance Amplifier Circuit 201,202 Measuring Instruments

Claims

1. A first transimpedance amplifier that converts current into voltage, The first transimpedance amplifier comprises at least one circuit block connected to the subsequent stage, Each of the aforementioned circuit blocks is: A conversion circuit that converts voltage to current, A transimpedance amplification circuit, comprising a second transimpedance amplifier connected downstream of the aforementioned conversion circuit, which converts current into voltage.

2. The transimpedance amplifier circuit according to claim 1, which feeds back at least one output of the circuit block.

3. The transimpedance amplifier circuit according to claim 2, wherein at least one output of the circuit block is fed back to the preceding stage of the first transimpedance amplifier.

4. The transimpedance amplifier circuit according to claim 2, wherein the output of the second transimpedance amplifier is fed back to part or all of the input of the second transimpedance amplifier and the input of at least one or more second transimpedance amplifiers located upstream of the second transimpedance amplifier.

5. The aforementioned conversion circuit is an emitter follower or a source follower, The transimpedance amplifier circuit according to any one of claims 1 to 4, wherein the second transimpedance amplifier is an RGC type transimpedance amplifier.

6. The conversion circuit is a transimpedance amplifier circuit according to any one of claims 1 to 4, wherein the conversion circuit converts voltage to current using a current mirror circuit.

7. The transimpedance amplifier circuit according to claim 6, wherein the current mirror circuit is a multicurrent mirror circuit.

8. A measuring instrument comprising a transimpedance amplifier circuit according to any one of claims 1 to 4.

9. A sensor that outputs current or charge via AC coupling is connected to the input of the first transimpedance amplifier, A comparator to which the output of the second transimpedance amplifier, which is included in the last stage circuit block of the aforementioned circuit block, is input, The measuring instrument according to claim 8, further comprising a counter for counting the output of the comparator.

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