Logarithmic amplifier

Abstract

A logarithmic amplifier (200) includes a logarithmic current preamplifier circuit (202) and a logarithmic amplifier circuit (204). The logarithmic current preamplifier circuit (202) includes an inverting input terminal (206A), an output terminal (206B), and a first diode (210). The first diode (210) is coupled between the inverting input terminal (206A) and the output terminal (206B) of the logarithmic current preamplifier circuit (202). The logarithmic amplifier circuit (204) includes an inverting input terminal (212A), an output terminal (212B), and a second diode (214). The inverting input terminal (212A) of the logarithmic amplifier circuit (204) is coupled to the output terminal (212B) of the logarithmic current preamplifier circuit (202). The second diode (214) is coupled between the inverting input terminal (212A) and the output terminal (212B) of the logarithmic amplifier circuit (204).

Description

Technical Field

[0001] This disclosure relates to logarithmic amplifiers. Background Technology

[0002] A logarithmic amplifier is an electronic circuit that produces an output signal with a value proportional to the logarithm of the input signal. Logarithmic amplifiers are used in many applications where signals with a large dynamic range are encountered, to compress wide dynamic range input signals. The outputs of photodiodes, ultrasonic receivers, and radar receivers are examples of signals that are sometimes compressed using logarithmic amplifiers. Summary of the Invention

[0003] This document discloses a logarithmic amplifier with high bandwidth and low settling time. In one example, a logarithmic amplifier includes a logarithmic current preamplifier circuit and a logarithmic amplifier circuit. The logarithmic current preamplifier circuit includes an inverting input terminal, an output terminal, and a first diode. The first diode is coupled between the inverting input terminal and the output terminal of the logarithmic current preamplifier circuit. The logarithmic amplifier circuit includes an inverting input terminal, an output terminal, and a second diode. The inverting input terminal of the logarithmic amplifier circuit is coupled to the output terminal of the logarithmic current preamplifier circuit. The second diode is coupled between the inverting input terminal and the output terminal of the logarithmic amplifier circuit.

[0004] In another example, a logarithmic amplifier includes a logarithmic current preamplifier circuit, a logarithmic amplifier circuit, a resistor, and a diode. The logarithmic current preamplifier circuit includes an output terminal. The logarithmic amplifier circuit includes an inverting input terminal. The resistor includes a first terminal coupled to the output terminal and a second terminal coupled to the inverting input terminal. The diode includes an anode terminal coupled to the output terminal and a cathode terminal coupled to the inverting input terminal.

[0005] In a further example, a circuit includes a first logarithmic current preamplifier circuit, a second logarithmic current preamplifier circuit, and a differential amplifier circuit. The differential amplifier circuit includes a non-inverting input terminal and an inverting input terminal. The non-inverting input terminal is coupled to the output terminal of the first logarithmic current preamplifier circuit. The inverting input terminal is coupled to the output terminal of the second logarithmic current preamplifier circuit. Attached Figure Description

[0006] To describe the various examples in detail, reference will now be made to the accompanying drawings, in which:

[0007] Figure 1 A schematic diagram of an example logarithmic amplifier is shown;

[0008] Figure 2 A schematic diagram of an example logarithmic amplifier including a logarithmic current preamplifier circuit according to the present disclosure is shown;

[0009] Figure 3A and 3B Demonstrates a circuit including a logarithmic amplifier according to this disclosure; and

[0010] Figure 4 A graph illustrating the bandwidth of the two logarithmic amplifiers is displayed. Detailed Implementation

[0011] In this description, the term "couple" refers to an indirect or direct wired or wireless connection. Therefore, if a first device is coupled to a second device, the connection can be a direct connection or an indirect connection via other devices and connections. Furthermore, in this description, the statement "based on" means "at least partially based on". Therefore, if X is based on Y, then X can vary depending on Y and any number of other factors.

[0012] Figure 1 A schematic diagram of an example logarithmic amplifier 100 is shown. The logarithmic amplifier 100 includes an amplifier 102 and a diode-connected transistor 104 in the feedback path of the amplifier 102. The base-emitter voltage (V) of the diode-connected transistor 104 is shown. BE This can be expressed as:

[0013]

[0014] in:

[0015] I IN It is the input current;

[0016] I S It is the reverse current of the PN junction of transistor 104, which is connected to a diode;

[0017] T is absolute temperature;

[0018] K is the Boltzmann constant; and

[0019] q is the charge of the electron.

[0020] V BE to I IN The logarithmic dependence spans five to six orders of magnitude from picoamperes to milliamperes.

[0021] Speed ​​is an important parameter of the logarithmic amplifier 100. With a small input current, the speed is affected by the base-emitter capacitance (C) of the transistor 104 connected by the diode. DThe time constant for the formation of the capacitor and its equivalent resistance is limited. The capacitance is defined by the emitter size.

[0022] The equivalent resistance of transistor 104 connected to the diode is:

[0023] (2)

[0024] Where n is the process dependency parameter.

[0025] With an input current of 100 nanoamperes (nA) (I IN In the case of R, E At 27°C, it is approximately 260 kΩ. This is comparable to the 0.5 to 1 picofarad C of most existing IC processes. D In the case of the actual value, this R E C D This limits the amplifier bandwidth to the range of 1 to 2 MHz. This limitation applies to any semiconductor process and is virtually independent of the transistor's bandwidth. t (The unity-gain frequency of the short-circuit current gain of the transistor).

[0026] The logarithmic amplifier disclosed herein increases operating speed and bandwidth by using a logarithmic current preamplifier to drive the logarithmic amplifier circuit. Figure 2 A schematic diagram of an example logarithmic amplifier 200, comprising a logarithmic current preamplifier circuit according to the present disclosure, is shown. The logarithmic amplifier 200 includes a logarithmic current preamplifier circuit 202, a logarithmic amplifier circuit 204, a diode 216, and a resistor 218. The logarithmic current preamplifier circuit 202 includes an amplifier 206, a resistor 208, and a diode 210. The amplifier 206 includes an inverting input terminal 206A coupled to a current source for receiving an input current to be converted into an output voltage logarithmically proportional to the input current.

[0027] The inverting input terminal 206A of amplifier 206 is coupled to the output terminal 206B of amplifier 206 via resistor 208 and diode 210. Terminal 208A of resistor 208 is coupled to the inverting input terminal 206A of amplifier 206, and terminal 208B of resistor 208 is coupled to the output terminal 206B of amplifier 206. The cathode terminal 210C of diode 210 is coupled to the inverting input terminal 206A of amplifier 206, and the anode terminal 210A of diode 210 is coupled to the output terminal 206B of amplifier 206. In some examples of the logarithmic current preamplifier circuit 202, diode 210 is implemented as a diode-connected transistor.

[0028] Logarithmic amplifier circuit 204 includes amplifier 212 and diode 214. Amplifier 212 includes an inverting input terminal 212A coupled to the output terminal 206B of amplifier 206. Inverting input terminal 206A is also coupled to the output terminal 212B of amplifier 212 via diode 214. The cathode terminal 214C of diode 214 is coupled to the output terminal 212B of amplifier 212, and the anode terminal 214A of diode 214 is coupled to the inverting input terminal 212A of amplifier 212. In some embodiments of logarithmic amplifier circuit 204, diode 214 is implemented as a diode-connected transistor.

[0029] Output terminal 206B is coupled to inverting input terminal 212A via diode 216 and resistor 218. The anode terminal 216A of diode 216 is coupled to output terminal 206B, and the cathode terminal 216C of diode 216 is coupled to inverting input terminal 212A. Terminal 218A of resistor 218 is coupled to output terminal 206B of amplifier 206, and terminal 218B of resistor 218 is coupled to inverting input terminal 212A of amplifier 212. In some embodiments of logarithmic amplifier 200, the resistance of resistor 208 is N times greater than the resistance of resistor 218, and the area of ​​diode 216 is several times larger than the area of ​​diode 210.

[0030] When I IN The voltage across resistor 208 is smaller than the voltage drop across diode 210 (I IN R0 <V BE When I IN The voltage flowing through resistor 208 and at the output terminal 206B of amplifier 206 is V1=I. IN R0. Therefore, when I IN When the current is less than the threshold current required to generate a voltage exceeding the voltage drop across resistor 208, I IN The current flows through resistor 208. The bandwidth of the logarithmic current preamplifier circuit 202 is through the pole (ROC) formed by the resistor and capacitor of diode 210. D Definition. The bandwidth of the logarithmic current preamplifier circuit 202 is large and independent of I. IN .

[0031] The current through resistor 218 (resistance R0 / N) is I IN N times larger. Diode 214 provides a logarithmic function (N*I) of the current traveling through resistor 218. INThe equivalent resistance of diode 214 decreases by a factor of N (due to current amplification) and the bandwidth of logarithmic amplifier circuit 204 increases by a factor of N. Therefore, using a small input current, the bandwidth of logarithmic amplifier 200 is established by resistors 208, 218, and diode 214, and current flows through resistors 208, 218, and diode 214. The N-fold gain adds some DC offset at the output of logarithmic amplifier 200, which can be achieved by... Figure 4 The circuit shown in the image features reverse channel compensation. ).

[0032] When I IN The voltage across resistor 208 is greater than the voltage drop across diode 210 (I IN R0>V BE When I IN The current flows through diode 210, and the voltage at the output terminal 206B of amplifier 206 is subject to a logarithmic function (V1 ~ log(I)). IN )) Limitations. Therefore, when I IN When the current is greater than the threshold current required to generate a voltage exceeding the voltage drop across resistor 208, I IN The current flows through diode 210. The logarithmic current preamplifier circuit 202 has a large bandwidth because the equivalent resistance of diode 210 is small (because of the large I). IN (and transconductance). The voltage (V1) at the output terminal 206B of amplifier 206 is converted into current by diode 216 with a gain set by the ratio of the resistance of diode 210 to the resistance of diode 216. Under these conditions, current flows in the path through diodes 210 and 216. A smooth transition from resistor ratio gain to diode area ratio gain is provided when Nx = N. Diode 214 provides a logarithmic function.

[0033] Figure 3AA circuit 300 incorporating a logarithmic amplifier according to this disclosure is shown. Circuit 300 includes a logarithmic current preamplifier circuit 301, a logarithmic current preamplifier circuit 303, a diode-connected transistor 314, a resistor 316, a diode-connected transistor 318, a resistor 320, and a differential amplifier circuit 321. The logarithmic current preamplifier circuit 301 and the differential amplifier circuit 321 form an embodiment of 200. Similarly, the logarithmic current preamplifier circuit 303 and the differential amplifier circuit 321 form an embodiment of 200. Circuit 300 generates a logarithmic output voltage as the difference between a first logarithmic signal generated by the logarithmic current preamplifier circuit 301 and the differential amplifier circuit 321 and a second logarithmic signal generated by the logarithmic current preamplifier circuit 303 and the differential amplifier circuit 321. In some applications, the inverting input terminal 302A of the logarithmic current preamplifier circuit 301 is coupled to a current source, such as a photodiode. In some embodiments of circuit 300, the non-inverting input terminal 302B of logarithmic current preamplifier circuit 301 is coupled to the non-inverting input terminal 304B of logarithmic current preamplifier circuit 303. In some applications, the inverting input terminal 304A of logarithmic current preamplifier circuit 303 is coupled to a current source, such as a photodiode or a reference current source.

[0034] The logarithmic current preamplifier circuit 301 includes an amplifier 302, a resistor 308, and a diode-connected transistor 306 coupled between the inverting input terminal 302A and the output terminal 302C of the logarithmic current preamplifier circuit 301. The resistor 308 and the diode-connected transistor 306 correspond to the amplifier 206, resistor 208, and diode 210 of the logarithmic current preamplifier circuit 302, respectively. The output terminal 302C of the logarithmic current preamplifier circuit 301 is coupled to the non-inverting input terminal 326A of the differential amplifier circuit 321 via a diode-connected transistor 314 and a resistor 316, which correspond to the diode 216 and resistor 218 of the logarithmic amplifier 200, respectively.

[0035] The logarithmic current preamplifier circuit 303 includes an amplifier 304, a resistor 312, and a diode-connected transistor 310 coupled between the inverting input terminal 304A and the output terminal 304C of the logarithmic current preamplifier circuit 303. The resistor 312 and the diode-connected transistor 310 correspond to the amplifier 206, resistor 208, and diode 210 of the logarithmic current preamplifier circuit 202, respectively. The output terminal 304C of the logarithmic current preamplifier circuit 303 is coupled to the inverting input terminal 326B of the differential amplifier circuit 321 via a diode-connected transistor 318 and a resistor 320, which correspond to the diode 216 and resistor 218 of the logarithmic amplifier 200, respectively.

[0036] The differential amplifier circuit 321 includes a differential amplifier 326, a diode-connected transistor 322, and a diode-connected transistor 324. The differential amplifier 326 corresponds to amplifier 212 of the logarithmic amplifier circuit 204, and the diode-connected transistors 322 and 324 correspond to diode 214 of the logarithmic amplifier circuit 204. The output terminal 326C of the logarithmic current preamplifier circuit 301 is coupled to the non-inverting input terminal 326A via the diode-connected transistor 322, and the output terminal 326D of the differential amplifier circuit 321 is coupled to the inverting input terminal 326B via the diode-connected transistor 324.

[0037] Therefore, as illustrated in circuit 300, in some circuits, diodes 210, 214, and 216 of the logarithmic amplifier 200 are implemented as diode-connected transistors.

[0038] Figure 3B A circuit 350 incorporating a logarithmic amplifier according to this disclosure is shown. Circuit 350 includes a logarithmic current preamplifier circuit 351, a logarithmic current preamplifier circuit 353, a base-grounded transistor 364, a resistor 366, a base-grounded transistor 368, a resistor 370, and a differential amplifier circuit 371. The logarithmic current preamplifier circuit 351 and the differential amplifier circuit 371 form an embodiment of a logarithmic amplifier 200. Similarly, the logarithmic current preamplifier circuit 353 and the differential amplifier circuit 371 form an embodiment of a logarithmic amplifier 200. Circuit 350 generates a logarithmic output voltage as the difference between a first logarithmic signal generated by the logarithmic current preamplifier circuit 351 and the differential amplifier circuit 371 and a second logarithmic signal generated by the logarithmic current preamplifier circuit 353 and the differential amplifier circuit 371. Circuit 350 is similar to circuit 300, but uses base-grounded transistors instead of diode-connected transistors 306, 310, 314 and 318 in circuit 300.

[0039] In some applications, the inverting input terminal 352A of the logarithmic current preamplifier circuit 351 is coupled to a current source, such as a photodiode. In some embodiments of circuit 350, the non-inverting input terminal 352B of the logarithmic current preamplifier circuit 351 is coupled to the non-inverting input terminal 354B of the logarithmic current preamplifier circuit 353. In some applications, the inverting input terminal 354A of the logarithmic current preamplifier circuit 353 is coupled to a current source, such as a photodiode or a reference current source.

[0040] The logarithmic current preamplifier circuit 351 includes amplifier 206, resistor 208, and diode 210 corresponding to the logarithmic current preamplifier circuit 202, respectively, amplifier 352, resistor 358, and base-grounded transistor 306. The output terminal 352C of the logarithmic current preamplifier circuit 351 is coupled to the non-inverting input terminal 376A of the differential amplifier circuit 371 via diode 216 and resistor 218 corresponding to the logarithmic amplifier 200, respectively.

[0041] The logarithmic current preamplifier circuit 353 includes an amplifier 206, a resistor 208, and a diode 210 corresponding to the logarithmic current preamplifier circuit 202, an amplifier 354, a resistor 362, and a base-to-ground transistor 360. The output terminal 354C of the logarithmic current preamplifier circuit 353 is coupled to the inverting input terminal 376B of the differential amplifier circuit 371 via a base-to-ground transistor 368 and a resistor 370 corresponding to the diode 216 and resistor 218 of the logarithmic amplifier 200, respectively.

[0042] The differential amplifier circuit 371 includes a differential amplifier 376, a diode-connected transistor 372, and a diode-connected transistor 374. The differential amplifier 376 corresponds to amplifier 212 of the logarithmic amplifier circuit 204, and the diode-connected transistors 372 and 374 correspond to diode 214 of the logarithmic amplifier circuit 204. The output terminal 376C of the differential amplifier circuit 371 is coupled to the non-inverting input terminal 376A via the diode-connected transistor 372, and the output terminal 376D of the differential amplifier circuit 371 is coupled to the inverting input terminal 376B via the diode-connected transistor 374.

[0043] Therefore, as described in circuit 350, in some circuits, diodes 210 and 216 of the logarithmic amplifier 200 are implemented as base-grounded transistors.

[0044] Figure 4A graph is shown illustrating the bandwidth of logarithmic amplifier 200 compared to the bandwidth of logarithmic amplifier 100. The bandwidth of logarithmic amplifier 200 is illustrated by curve 402, and the bandwidth of logarithmic amplifier 100 is illustrated by curve 404. Figure 4 The demonstration showed that the bandwidth of the 200 was significantly higher than (for example, more than 10 times higher) than that of the logarithmic amplifier 100.

[0045] Within the scope of the claims, modifications to the described embodiments are possible, and other embodiments are also possible.

Claims

1. A logarithmic amplifier, comprising: Logarithmic current preamplifier circuit, which includes: Inverting input terminal; Output terminals; A first diode, coupled between the inverting input terminal and the output terminal; and The first resistor includes: The first terminal is coupled to the output terminal of the logarithmic current preamplifier circuit; and The second terminal is coupled to the inverting input terminal of the logarithmic current preamplifier circuit; and A logarithmic amplifier circuit includes: The inverting input terminal is coupled to the output terminal of the logarithmic current preamplifier circuit; Output terminals; and A second diode is coupled between the inverting input terminal and the output terminal of the logarithmic amplifier circuit.

2. The logarithmic amplifier according to claim 1, wherein: The cathode terminal of the first diode is coupled to the inverting input terminal of the logarithmic current preamplifier circuit; and The anode terminal of the first diode is coupled to the output terminal of the logarithmic current preamplifier circuit.

3. The logarithmic amplifier according to claim 1, wherein: The anode terminal of the second diode is coupled to the inverting input terminal of the logarithmic amplifier circuit; and The cathode terminal of the second diode is coupled to the output terminal of the logarithmic amplifier circuit.

4. The logarithmic amplifier according to claim 1, further comprising: The third diode includes: The anode terminal, coupled to the output terminal of the logarithmic current preamplifier circuit; and The cathode terminal is coupled to the inverting input terminal of the logarithmic amplifier circuit.

5. The logarithmic amplifier according to claim 1, further comprising: The second resistor includes: The first terminal is coupled to the output terminal of the logarithmic current preamplifier circuit; and The second terminal is coupled to the inverting input terminal of the logarithmic amplifier circuit.

6. The logarithmic amplifier according to claim 1, wherein: A first current flows from the inverting input terminal of the logarithmic current preamplifier circuit through the first resistor to the output terminal of the logarithmic current preamplifier circuit based on the first current being less than a threshold. and The second current flows from the inverting input terminal of the logarithmic current preamplifier circuit through the first diode to the output terminal of the logarithmic current preamplifier circuit, based on the second current being greater than the threshold.

7. A logarithmic amplifier, comprising: Logarithmic current preamplifier circuit, which includes: Output terminals; Inverting input terminal; The first diode includes: Anode terminal, which is coupled to the output terminal; and The cathode terminal, coupled to the inverting input terminal of the logarithmic current preamplifier circuit; and The first resistor includes: A first terminal, which is coupled to the output terminal; and The second terminal is coupled to the inverting input terminal of the logarithmic current preamplifier circuit; and A logarithmic amplifier circuit includes: Inverting input terminal; The second resistor includes: A first terminal, which is coupled to the output terminal; and The second terminal, which is coupled to the inverting input terminal; and The second diode includes: Anode terminal, which is coupled to the output terminal; and The cathode terminal is coupled to the inverting input terminal.

8. The logarithmic amplifier according to claim 7, wherein: The logarithmic amplifier circuit includes: Output terminals; and The third diode includes: A cathode terminal, coupled to the output terminal of the logarithmic amplifier circuit; and The anode terminal is coupled to the inverting input terminal of the logarithmic amplifier circuit.

9. The logarithmic amplifier according to claim 7, wherein: The area of ​​the second diode is N times larger than the area of ​​the first diode; and The resistance of the first resistor is N times higher than that of the second resistor.

10. The logarithmic amplifier according to claim 7, wherein: A first current flows from the inverting input terminal of the logarithmic current preamplifier circuit through the first diode to the output terminal, based on a first voltage across the first resistor being greater than the voltage drop across the first diode. and The second current flows from the inverting input terminal of the logarithmic current preamplifier circuit through the first resistor to the output terminal, based on a second voltage across the first resistor being less than the voltage drop across the first diode.

11. A circuit comprising: The first logarithmic current preamplifier circuit includes: Inverting input terminal; Output terminals; A first diode, coupled between the inverting input terminal and the output terminal of the first logarithmic current preamplifier circuit; and A first resistor is coupled between the inverting input terminal and the output terminal of the first logarithmic current preamplifier circuit; The second logarithmic current preamplifier circuit includes: Inverting input terminal; Output terminals; A second diode, coupled between the inverting input terminal and the output terminal of the second logarithmic current preamplifier circuit; and A second resistor is coupled between the inverting input terminal and the output terminal of the second logarithmic current preamplifier circuit; and A differential amplifier circuit includes: The non-inverting input terminal is coupled to the output terminal of the first logarithmic current preamplifier circuit; and The inverting input terminal is coupled to the output terminal of the second logarithmic current preamplifier circuit.

12. The circuit of claim 11, wherein the differential amplifier circuit includes a diode coupled between the non-inverting input terminal of the differential amplifier circuit and the output terminal of the differential amplifier circuit.

13. The circuit of claim 11, wherein the differential amplifier circuit includes a diode coupled between the inverting input terminal of the differential amplifier circuit and the output terminal of the differential amplifier circuit.

14. The circuit of claim 11, further comprising: A third diode is coupled between the output terminal of the first logarithmic current preamplifier circuit and the non-inverting input terminal of the differential amplifier circuit. and A third resistor is coupled between the output terminal of the first logarithmic current preamplifier circuit and the non-inverting input terminal of the differential amplifier circuit.

15. The circuit of claim 11, further comprising: A fourth diode is coupled between the output terminal of the second logarithmic current preamplifier circuit and the inverting input terminal of the differential amplifier circuit; and A fourth resistor is coupled between the output terminal of the second logarithmic current preamplifier circuit and the inverting input terminal of the differential amplifier circuit.

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