Electronic amplifier

Abstract

Embodiments of the present disclosure relate to electronic amplifiers. A variable gain amplifier has a cascode stage formed by a pair of cross-coupled transistors. Each pair of cross-coupled transistors is provided with a transformer that keeps the impedance presented to the cross-coupled transistors constant with gain.

Description

Technical Field

[0001] This disclosure relates to an electronic amplifier and an apparatus comprising the electronic amplifier. Background Technology

[0002] A variable gain amplifier is an electronic amplifier that dynamically adjusts its gain based on an external control signal. This allows for precise control of the amplitude of the amplifier's output signal. These types of electronic amplifiers are used in applications requiring a large dynamic range, such as audio processing, communication systems, and signal conditioning.

[0003] However, in high-frequency applications, the response of an electronic amplifier is inconsistent across different gain settings, resulting in inconsistent frequency responses across all gains. Since the electronic amplifier is part of an electronic system (e.g., a receiver or transmitter), signal integrity must be ensured under all conditions. If the frequency response of the electronic amplifier varies with gain, other components in the electronic system, such as equalizers or digital signal processors, whose parameters have been fine-tuned to provide signal integrity at a specific gain, will be unable to ensure proper signal integrity at different gains.

[0004] In the context of this disclosure, when an electronic amplifier operates at frequencies above several hundred megahertz or several kilohertz or higher, the application (i.e., the implementation context) is referred to as "high frequency". For example, electronic amplifiers used in telecommunications systems (5G, WiFi, satellite communications), optical systems (data communications, telecommunications), radar systems, test and equipment, and / or medical systems are electronic amplifiers used in high frequency applications.

[0005] The purpose of this disclosure is to overcome one or more of the limitations described above. Summary of the Invention

[0006] According to a first aspect of this disclosure, an electronic amplifier is provided, comprising: a first transistor including a first terminal and a second terminal; a second transistor including a third terminal and a fourth terminal; a first pair of cross-coupled transistors including a third transistor and a fourth transistor, the first pair of cross-coupled transistors being connected to the second terminal; a second pair of cross-coupled transistors including a fifth transistor and a sixth transistor, the second pair of cross-coupled transistors being connected to the fourth terminal, the first pair of cross-coupled transistors and the second pair of cross-coupled transistors forming a common-source, common-gate stage; a first transformer; and a second transformer; wherein the first transformer is coupled between the second terminal and the first pair of cross-coupled transistors, and the second transformer is coupled between the fourth terminal and the second pair of cross-coupled transistors, such that the first transformer and the second transformer provide impedance to the common-source, common-gate stage, the impedance being configured to be substantially constant for different gains when the electronic amplifier operates at high frequencies.

[0007] Alternatively, the electronic amplifier is a variable gain amplifier.

[0008] Alternatively, the variable gain amplifier is a Gilbert unit, a differential variable gain amplifier, and / or a single-ended variable gain amplifier.

[0009] Optionally, the first transistor and the second transistor form a first pair of differential transistors.

[0010] Optionally, the first transistor and / or the second transistor includes one of the following: a bipolar junction transistor, a field-effect transistor (FET), a heterojunction bipolar transistor, a junction FET, a metal-oxide-semiconductor FET, an insulated gate bipolar transistor, a metal-semiconductor FET, a high electron mobility transistor, a fin FET, or a tunnel FET.

[0011] Optionally, one or each of the transistors forming the first pair of cross-coupled transistors and the second pair of cross-coupled transistors includes one of the following: bipolar junction transistor, field-effect transistor (FET), heterojunction bipolar transistor, junction FET, metal-oxide-semiconductor FET, insulated gate bipolar transistor, metal-semiconductor FET, high electron mobility transistor, fin FET, or tunnel FET.

[0012] Optionally, the first transformer includes a first pair of coupled spiral inductors, and the second transformer includes a second pair of coupled spiral inductors.

[0013] Optionally, the first pair of coupled spiral inductors has an orientation configured to generate a first high-frequency impedance.

[0014] Optionally, the second pair of coupled spiral inductors has an orientation configured to generate a second high-frequency impedance.

[0015] According to a first aspect of this disclosure, an apparatus is provided comprising an electronic amplifier including: a first transistor including a first terminal and a second terminal; a second transistor including a third terminal and a fourth terminal; a first pair of cross-coupled transistors including a third transistor and a fourth transistor, the first pair of cross-coupled transistors being connected to the second terminal; a second pair of cross-coupled transistors including a fifth transistor and a sixth transistor, the second pair of cross-coupled transistors being connected to the fourth terminal, the first pair of cross-coupled transistors and the second pair of cross-coupled transistors forming a common-source, common-gate stage; a first transformer; and a second transformer; wherein the first transformer is coupled between the second terminal and the first pair of cross-coupled transistors, and the second transformer is coupled between the fourth terminal and the second pair of cross-coupled transistors, such that the first transformer and the second transformer provide impedance to the common-source, common-gate stage, the impedance being configured to be substantially constant for different gains when the electronic amplifier operates at a high frequency.

[0016] Optionally, the device includes any one of the following: an audio processing system; a communication system; a signal conditioning system. Attached Figure Description

[0017] The present disclosure will now be described in further detail by way of example only with reference to the accompanying drawings, in which:

[0018] Figure 1 This is an example of an electronic amplifier based on existing technology;

[0019] Figure 2 This is a first example embodiment of the electronic amplifier according to the present disclosure;

[0020] Figure 3 Examples of devices including electronic amplifiers according to this disclosure; and

[0021] Figure 4 This is an exemplary embodiment of an apparatus that includes an electronic amplifier according to the present disclosure. Detailed Implementation

[0022] The most common implementation in the field of variable gain electronic amplifiers is the Gilbert unit. The Gilbert unit is a differential amplifier configuration that utilizes a balanced mixer design to achieve linearly controllable gain variation.

[0023] Figure 1 This is an example of a Gilbert cell 100 according to the prior art. The Gilbert cell 100 includes a pair of differential transistors Q1 and Q2. In this example of the prior art, the pair of differential transistors Q1 and Q2 are bipolar junction transistors (BJTs) including emitter, base, and collector. A positive input signal In+ is fed to the base of BJT Q1, while a negative input signal In- is fed to the base of BJT Q2. The emitters of BJTs Q1 and Q2 are connected to a common tail current source Idc.

[0024] Gilbert cell 100 also includes a first pair of cross-coupled transistors Q3, Q5 and a second pair of cross-coupled transistors Q4, Q6, collectively referred to as a common-source, common-gate stage. In this prior art example, the first pair of cross-coupled transistors Q3, Q5 and the second pair of cross-coupled transistors Q4, Q6 are bipolar junction transistors (BJTs), each BJT including an emitter, a base, and a collector. The emitters of the first pair of cross-coupled transistors Q3, Q5 are coupled to the collector of the BJT Q1, while the emitters of the second pair of cross-coupled transistors Q4, Q6 are coupled to the collector of the BJT Q2. The collectors of the first pair of cross-coupled transistors Q3, Q5 and the second pair of cross-coupled transistors Q4, Q6 are coupled to loads R1 and R2. In an alternative embodiment, the load may be a resistor selectively connected in parallel with a capacitor, an inductor, or a combination of these elements.

[0025] In operation, the differential current generated by the pair of differential transistors Q1 and Q2 is fed to the first pair of cross-coupled transistors Q3 and Q5 and the second pair of cross-coupled transistors Q4 and Q6. The percentage of current flowing into the loads R1 and R2 is determined by control voltages VGC and VGCB. Control voltage VGC is input to the bases of bipolar transistors Q3 and Q4, while control voltage VGCB is fed to the bases of bipolar transistors Q5 and Q6. Control voltages VGC and VGCB determine the percentage of collector current of Q1 and Q2 that will be introduced into the loads R1 and R2. Therefore, control voltages VGC and VGCB determine the gain of the Gilbert cell 100.

[0026] When the control voltage VGC is at its maximum and the control voltage VGCB is at its minimum, all current from the collectors of bipolar junction transistors Q1 and Q2 flows into the loads R1 and R2. This is known as maximum gain. When the control voltage VGC decreases and the control voltage VGCB increases, a portion of the current from the collectors of bipolar junction transistors Q1 and Q2 is redirected from the load branches Q3 and Q4 to the dummy branch Q5, causing a decrease in the gain of the Gilbert cell 100.

[0027] One issue with the Gilbert Unit 100 is that its frequency response is inconsistent across different gain settings during high-frequency applications. This problem is exacerbated between maximum and low gain. This is a consequence of the impedance of the cascode stage varying with gain.

[0028] During maximum gain, the emitter impedances of bipolar junction transistors Q3 and Q4 toward the cascode stage are given by the base-emitter capacitance impedance Cbe of Q3 and Q4 in parallel with the following equation:

[0029]

[0030] Where V t It is thermal voltage, I c This is the current emitted from the collectors of bipolar junction transistors Q1 and Q2. The base-emitter capacitance impedance Cbe is due to the depletion layer modulation and diffusion capacitance, and increases with I... c The impedance increases with the increase of R. At low frequencies, the impedance of the emitters of Q3 and Q4 increases due to the increase of R. e Under normal conditions, the impedance is dominated by Cbe, while under high-frequency operation, it is dominated by Cbe. Bipolar junction transistors Q5 and Q6 are turned off and behave as open circuits with extremely high impedance because there is no conduction between the emitter and collector of Q5 and Q6. Since transistors Q5 and Q6 are turned off, the leakage capacitance from these transistors does not significantly affect the circuit conductance, thus the total impedance remains high. Under low-gain conditions, Q5 and Q6 are turned on. Therefore, the impedance of Q5 and Q6 to the emitter is in parallel with Cbe, changing from high to R. eWhere Cbe follows I c The impedance variation between the maximum and low gain results affects the frequency response of the Gilbert unit 100, causing different frequency responses between different gains, which is undesirable for ensuring signal integrity.

[0031] It is desirable to provide an electronic amplifier that reduces the effect of the base-emitter capacitance (Cbe) of one or more transistors in the cascode stage (Q3, Q4, Q5, and Q6) of a variable gain amplifier, so as to make the frequency response of the electronic amplifier more uniform at both maximum and low gain.

[0032] Figure 2 This is an example embodiment of the electronic amplifier 200 according to the present disclosure. The electronic amplifier 200 includes a first transistor Q1” and a second transistor Q2”. The first transistor Q1” includes terminals 202, 203, and 204, which include a first terminal 202 and a second terminal 204. The second transistor Q2” includes terminals 205, 206, and 207, which include a third terminal 205 and a fourth terminal 207. The first transistor Q1” and the second transistor Q2” form a first pair of differential transistors. In this example embodiment, the first transistor Q1” and the second transistor Q2” are bipolar junction transistors, the first terminal 202 is the base of Q1”, the second terminal 204 is the collector of Q1”, the third terminal 205 is the base of Q2”, and the fourth terminal 207 is the collector of Q2”.

[0033] In alternative embodiments, as understood by those skilled in the art, the first transistor Q1” and the second transistor Q2” can be field-effect transistors (FETs), heterojunction bipolar transistors (HBTs), junction FETs, metal-oxide-semiconductor FETs, insulated-gate bipolar transistors (IGBTs), metal-semiconductor FETs, high electron mobility transistors (HEMTs), fin FETs, and / or tunnel FETs. The electronic amplifier 200 can be, for example, a variable gain amplifier. In particular, but not limited to, it can be a Gilbert unit. In alternative embodiments, the electronic amplifier 200 can be other types of differential and single-ended Gilbert unit-type variable gain amplifiers (VGAs).

[0034] The electronic amplifier 200 also includes a first pair of cross-coupled transistors Q3” and Q5”, which includes a third transistor Q3” and a fourth transistor Q5”. The third transistor Q3” and the fourth transistor Q5” are coupled to the first transistor Q1 via the second terminal 204. The electronic amplifier also includes a second pair of cross-coupled transistors Q4” and Q6”, which includes a fifth transistor Q4” and a sixth transistor Q6”. The fifth transistor Q4” and the sixth transistor Q6” are coupled to the second transistor Q2 via the fourth terminal 207. The first pair of cross-coupled transistors Q3”, Q5” and the second pair of cross-coupled transistors Q4”, Q6” form a common-source, common-gate stage of the electronic amplifier 200. Figure 2 In the example embodiment, the third transistor Q3”, the fourth transistor Q5”, the fifth transistor Q4”, and the sixth transistor Q6” are bipolar junction transistors. However, as those skilled in the art will understand, in alternative embodiments, they may be field-effect transistors (FETs), heterojunction bipolar transistors (HBTs), junction FETs, metal-oxide-semiconductor FETs, insulated-gate bipolar transistors (IGBTs), metal-semiconductor FETs, high electron mobility transistors (HEMTs), fin FETs, and / or tunnel FETs.

[0035] The electronic amplifier 200 includes loads R1” and R2”. In an alternative embodiment, as understood by those skilled in the art, the loads may be resistors connected in parallel with a capacitor, an inductor, or any combination of these circuit elements.

[0036] The electronic amplifier 200 also includes a first transformer 210 and a second transformer 220. The first transformer 210 is coupled between the second terminal 204 of the first transistor Q1” and the first pair of cross-coupled transistors Q3” and Q5”, while the second transformer Q2” is coupled between the fourth terminal 207 of the second transistor Q2” and the second pair of cross-coupled transistors Q4” and Q6”. Both the first transformer 210 and the second transformer 220 are configured to provide impedance to the cascode stages Q3”, Q5” and Q4”, Q6”, which is substantially constant for different amplifier gains when the electronic amplifier 200 operates under high-frequency conditions. In this example embodiment, the first transformer 210 is formed by a first pair of coupled spiral inductors L1 and L2, while the second transformer 220 is formed by a second pair of coupled spiral inductors L3 and L4.

[0037] In operation, the first pair of coupled spiral inductors L1 and L2 and the second pair of coupled spiral inductors L3 and L4 are oriented in such a way that at a given frequency The high-frequency impedance Ze of the downward-facing spiral inductor L2 (L4) is given by the following formula:

[0038]

[0039] L1 (L3) and L2 (L4) are the inductors of the first (second) coupled spiral inductor. This is one of the operating frequencies of the electronic amplifier 200, k is the coupling coefficient between spirals L1 and L2 (L3 and L4), ie3 is the RF (radio frequency) Q3” emitter current flowing into L1, ie5 is the RF Q5” emitter current flowing into L2, and Cbe5 is the emitter-base capacitance of Q5”. If the gain increases, the current through Q5” decreases, therefore Cbe5 decreases, and the fractional... Increase. Therefore, the impedance due to mutual inductance increases. The gain will increase as more current flows into Q3” and less current flows into Q5”. Therefore, the change in impedance Ze decreases as the gain increases. If the gain decreases, the current flowing into Q3” decreases, therefore Cbe3 decreases, and thus the fractional... Increase. Through mutual inductance of L1 The gain increases, thus reducing the change in impedance Ze as the gain decreases.

[0040] In the context of this disclosure, orienting the first pair of coupled spiral inductors L1 and L2 and the second pair of coupled spiral inductors L3 and L4 means that the spiral inductors L1 and L2 (L3 and L4) are coupled such that the current flowing in one spiral L1 (L3) generates a current flowing in a first direction, which is opposite to the direction of the current flowing in the other spiral L2 (L4).

[0041] The first transformer 210 and the second transformer 220 provide impedances from the second terminal 204 of Q1” and the fourth terminal 207 of Q2” to the cascode stage, which have substantially constant gain at high frequencies. This is achieved by keeping the impedances presented to the first pair of cross-coupled transistors Q3”, Q5” and the second pair of cross-coupled transistors Q4”, Q6” constant with gain.

[0042] Figure 3 This is an example device 300 according to the present disclosure. Device 300 includes the electronic amplifier 200 of the present disclosure. Device 300 may be, for example, a communication system, an audio processing system, and / or a signal conditioning system.

[0043] Figure 4 This is an exemplary embodiment of a device 400 including the electronic amplifier 200 of this disclosure. In this exemplary embodiment, device 400 is an optical communication system. The optical communication system 400 includes a transimpedance amplifier (TIA), a digital signal processor (DSP), and a photodetector (PD). The TIA includes an input amplifier, an output amplifier, and the electronic amplifier 200 of this disclosure.

[0044] In operation, the TIA amplifies the current received from the PD into a voltage for subsequent processing by, for example, a DSP. The TIA's output is kept constant by an automatic gain control loop that adjusts the gain of the electronic amplifier 200 based on the amplitude of the TIA's input current. The DSP's parameters are calibrated so that the overall frequency response of the PD, TIA, and DSP is optimal for signal integrity. If the TIA's frequency response varies with the gain of the electronic amplifier 200, the frequency response of the entire optical communication system will no longer be optimal for signal integrity.

[0045] It should be understood that the electronic amplifier disclosed herein may be a Gilbert unit for use in variable gain amplification systems.

[0046] Those skilled in the art will understand that variations of the disclosed arrangements are possible without departing from this disclosure. Therefore, the above description of specific embodiments is merely exemplary and not intended to be limiting. It will be apparent to those skilled in the art that minor modifications can be made without significantly altering the described operation.

[0047] In particular, it will be noted that the polarity of general components can be reversed; that is, an npn transistor can alternatively be implemented as a pnp transistor, and this disclosure is not limited to any particular polarity. Furthermore, references to components “coupled” to each other do not require a direct physical connection; a suitable example is the coupling of the second terminal 204 to a pair of cascode transistors Q3”, Q5”, and the coupling of the fourth terminal 207 to a pair of cascode transistors Q4”, Q6”, each implemented via insertion transformers 210, 220. These components are coupled to each other because the state of one component directly affects the other. Unless explicitly stated otherwise, the term “connected” may also be used in a similar sense to “coupled.”

Claims

1. An electronic amplifier, comprising: The first transistor includes a first terminal and a second terminal; The second transistor includes a third terminal and a fourth terminal; The first pair of cross-coupled transistors includes a third transistor and a fourth transistor, and the first pair of cross-coupled transistors is connected to the second terminal; The second pair of cross-coupled transistors, including a fifth transistor and a sixth transistor, are connected to the fourth terminal. The first pair of cross-coupled transistors and the second pair of cross-coupled transistors form a common source and common gate circuit. First transformer; as well as Second transformer, The first transformer is coupled between the second terminal and the first pair of cross-coupled transistors, and the second transformer is coupled between the fourth node and the second pair of cross-coupled transistors, such that the first transformer and the second transformer provide impedance to the cascode stage, the impedance being configured to be substantially constant for different gains when the electronic amplifier operates at high frequencies.

2. The electronic amplifier according to claim 1 is a variable gain amplifier.

3. The electronic amplifier according to claim 2, wherein the variable gain amplifier is a Gilbert unit, a differential variable gain amplifier, and / or a single-ended variable gain amplifier.

4. The electronic amplifier of claim 1, wherein the first transistor and the second transistor form a first pair of differential transistors.

5. The electronic amplifier according to claim 4, wherein: The first transistor and / or the second transistor includes one of the following: a bipolar junction transistor; a field-effect transistor (FET); a heterojunction bipolar transistor; Junction FET; Metal-Oxide-Semiconductor FET; Insulated Gate Bipolar Transistor; Metal-Semiconductor FET; High Electron Mobility Transistor; Fin-type FET; And tunnel FET.

6. The electronic amplifier according to claim 1, wherein: One or each of the transistors forming the first pair of cross-coupled transistors and the second pair of cross-coupled transistors includes one of the following: a bipolar junction transistor; a field-effect transistor; a heterojunction bipolar transistor; Junction FET; Metal-Oxide-Semiconductor FET; Insulated Gate Bipolar Transistor; Metal-Semiconductor FET; High Electron Mobility Transistor; FinFET; and Tunnel FET.

7. The electronic amplifier of claim 1, wherein the first transformer comprises a first pair of coupled spiral inductors, and the second transformer comprises a second pair of coupled spiral inductors.

8. The electronic amplifier of claim 7, wherein the first pair of coupled spiral inductors has an orientation configured to generate a first high-frequency impedance.

9. The electronic amplifier of claim 7, wherein the second pair of coupled spiral inductors has an orientation configured to generate a second high-frequency impedance.

10. An apparatus comprising: Electronic amplifiers, including: The first transistor includes a first terminal and a second terminal; The second transistor includes a third terminal and a fourth terminal; The first pair of cross-coupled transistors includes a third transistor and a fourth transistor, and the first pair of cross-coupled transistors is connected to the second terminal; The second pair of cross-coupled transistors, including a fifth transistor and a sixth transistor, are connected to the fourth terminal. The first pair of cross-coupled transistors and the second pair of cross-coupled transistors form a common source and common gate circuit. load; The first transformer; and Second transformer, The first transformer is coupled between the second terminal and the first pair of cross-coupled transistors, and the second transformer is coupled between the fourth node and the second pair of cross-coupled transistors, such that the first transformer and the second transformer provide impedance to the cascode stage, the impedance being configured to be substantially constant for different gains when the electronic amplifier operates at high frequencies.

11. The apparatus of claim 10, comprising any one of the following: Audio processing system; Communication systems; and Signal conditioning system.

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