A broadband transimpedance amplifier spike cancellation circuit

Abstract

This invention discloses a broadband transimpedance amplifier spike cancellation circuit, including a main amplification stage, a feedback network, and an automatic gain control circuit. The main amplification stage has an input terminal VI and an output terminal VO. The feedback network includes a feedback resistor R1 and a dynamically adjustable feedback network. The feedback resistor R1 is the main feedback element used to set the basic gain of the transimpedance amplifier. The dynamically adjustable feedback network is connected in parallel with the feedback resistor R1 and includes a MOSFET M1 and a series resonant network. The series resonant network includes an inductor L2, a MOSFET M2, and a capacitor C2 connected in series. The automatic gain control circuit can output a control voltage VFB according to the intensity of the input optical signal to dynamically adjust the on-resistance of MOSFETs M1 and M2. This invention introduces a Q-controllable series resonant network at the feedback terminal of a traditional transimpedance amplifier, introducing an in-band reverse resonant point to eliminate in-band frequency response spikes. Furthermore, it achieves optimized in-band flatness under different light intensities, optimizing signal quality and communication stability.

Description

Technical Field

[0001] This invention relates to microelectronics technology, and in particular to a broadband transimpedance amplifier spike cancellation circuit. Background Technology

[0002] In the front-end of an optical receiver, the transimpedance amplifier (TIA) converts and amplifies the current signal output from a photodiode (PD) or avalanche photodiode (APD) into a voltage signal before sending it to subsequent amplifier stages for processing. As a core amplification stage, the TIA's transimpedance gain, noise, sensitivity, in-band flatness, and overload performance have a significant impact on the overall performance of the receiver system.

[0003] The parasitic capacitance of a photodiode or avalanche photodiode, along with the bonding wire inductance connected to the transimpedance amplifier, creates a resonant point. This resonant point forms a spike in the in-band frequency response curve of the transimpedance amplifier, which significantly affects its in-band flatness and may also impact its stability. Therefore, spike cancellation techniques for transimpedance amplifiers are crucial for their bandwidth and sensitivity performance.

[0004] Traditional transimpedance amplifiers, due to their low bandwidth, typically improve in-band flatness by placing the resonant peak out of band. However, with the development of optical communication technology and the increase in communication speed, high-bandwidth transimpedance amplifiers are increasingly needed in various applications. As transimpedance amplifiers switch from high-gain to low-gain settings, the impact of in-band peaks becomes increasingly significant. Therefore, achieving fully dynamic in-band flatness optimization in broadband applications has become a pressing need for more and more applications. Summary of the Invention

[0005] The technical problem this invention aims to solve is to address the shortcomings of the prior art by providing a broadband transimpedance amplifier spike cancellation circuit. This circuit introduces a Q-controllable series resonant network at the feedback terminal of a conventional transimpedance amplifier, thereby introducing an in-band inverse resonant point and eliminating in-band frequency response spikes. Simultaneously, it achieves optimized in-band flatness under varying light intensities, thus improving signal quality and communication stability.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A broadband transimpedance amplifier spike cancellation circuit includes a main amplification stage, a feedback network, and an automatic gain control circuit.

[0008] The main amplifier stage has an input terminal VI and an output terminal VO; the input terminal VI is used to receive the current signal from the external photodiode, and the output terminal VO is used to output the amplified voltage signal.

[0009] The feedback network includes the feedback resistor R1 and the dynamically adjustable feedback network.

[0010] The feedback resistor R1 is the main feedback element, used to set the basic gain of the transimpedance amplifier.

[0011] The dynamic adjustment feedback network is connected in parallel with the feedback resistor R1, and includes the MOSFET M1 and the series resonant network.

[0012] The series resonant network consists of an inductor L2, a MOSFET M2, and a capacitor C2 connected in series.

[0013] The automatic gain control circuit can output a control voltage VFB according to the intensity of the input optical signal, and dynamically adjust the on-resistance of MOSFETs M1 and M2.

[0014] The series resonant frequency of inductor L2 and capacitor C2 is configured to be the same as or close to the parasitic resonant frequency formed by the parasitic capacitance of the external photodiode and the inductance of the bond wire, and the on-resistance of MOSFET M2 determines the quality factor Q of the series resonant network.

[0015] The source of MOSFET M1 is connected to the input terminal VI, the drain of MOSFET M1 is connected to the positive terminal of inductor L2, the negative terminal of inductor L2 is connected to the drain of MOSFET M2, and the source of MOSFET M2 is connected to the input terminal VI via capacitor C2, thereby forming the dynamic adjustment feedback network.

[0016] The main amplification stage includes transistors Q1, Q2, and Q3, MOSFET M3, capacitor C1, and resistor R2.

[0017] The base of transistor Q1, the source of MOSFET M1, the lower plate of capacitor C2, the positive terminal of resistor R1, and the upper plate of capacitor C1 are all connected to the input terminal VI.

[0018] The upper plate of capacitor C1 is connected to the source of MOSFET M2; the drain of MOSFET M2 is connected to the negative terminal of inductor L2; the drain of MOSFET M1, the positive terminal of inductor L2, the collector of transistor Q1, and the emitter of transistor Q2 are connected.

[0019] The collector of transistor Q2, the negative terminal of resistor R2, the base of transistor Q3, and the output terminal VO are connected; the positive terminal of resistor R2 is connected to the collector of transistor Q3 and to the power supply; the emitter of transistor Q3, the collector of MOSFET M3, the negative terminal of resistor R1, and the lower plate of capacitor C1 are all connected to the negative input terminal of the automatic gain control circuit, which can reflect the intensity of the input optical signal; the gate of MOSFET M3 is connected to a fixed bias VBN and is used as a tail current source; the output terminal of the automatic gain control circuit is connected to the gates of MOSFETs M1 and M2.

[0020] The automatic gain control circuit includes an error amplifier, whose positive input is connected to the reference voltage Vref, its negative input is Vsense, and its output is a control voltage VFB after passing through a low-pass filter.

[0021] The error amplifier compares Vsense with Vref, thereby dynamically adjusting the transimpedance gain, specifically:

[0022] When Vsense < Vref, the input optical signal is weak, the control voltage VFB decreases, so that both MOSFETs M1 and M2 are in the cutoff region, and the feedback resistor R1 is the only feedback element. At this time, the transimpedance gain TZ = R1.

[0023] When Vsense≥Vref, the input optical signal is strong light, and the control voltage VFB increases, causing both MOSFETs M1 and M2 to operate in the linear region. The on-resistance of MOSFETs M1 and M2 is controlled by the control voltage VFB. The series resonant network is connected to the feedback path, generating a gain dip at the series resonant frequency of inductor L2 and capacitor C2, eliminating the frequency response spike caused by the parasitic resonance of the external photodiode.

[0024] When the input optical signal is strong light, the expression for the transimpedance gain TZ is:

[0025]

[0026] In the formula, RM1 is the on-resistance of MOSFET M1, RM2 is the on-resistance of MOSFET M2, gm2 is the transconductance of transistor Q2, s is the complex frequency; C2 is the capacitance of capacitor C2; L2 is the inductance of inductor L2; R2 is the resistance of resistor R2; the symbol "||" indicates the parallel summation of the impedance values ​​before and after the symbol.

[0027] The size of MOSFET M2 is selected such that the quality factor Q of the series resonant network matches the quality factor Q of the external parasitic resonant network where the external photodiode is located, thereby achieving the best peak elimination effect under different process and packaging conditions.

[0028] The broadband transimpedance amplifier spike cancellation circuit is integrated into a single chip, and the input terminal VI is used to connect an external photodiode or avalanche photodiode.

[0029] The present invention has the following beneficial effects:

[0030] 1. This invention introduces a Q-controllable series resonant network at the feedback end of a traditional transimpedance amplifier, thereby introducing an in-band reverse resonant point, eliminating in-band frequency response spikes, and achieving better in-band flatness.

[0031] 2. This invention can achieve optimal in-band flatness under different light intensities, and also has better performance in terms of temporal eye diagram, signal quality and stability. Attached Figure Description

[0032] Figure 1 The circuit diagram of a broadband transimpedance amplifier spike cancellation circuit according to the present invention is shown.

[0033] Figure 2 The circuit diagram of a conventional transimpedance amplifier is shown.

[0034] Figure 3 The transimpedance gain frequency response curve of the present invention is shown.

[0035] Figure 4 The frequency response curves of the cascaded photodiode and transimpedance amplifier are shown.

[0036] Figure 5 The frequency response curves of a conventional transimpedance amplifier at different light intensities are shown.

[0037] Figure 6 The frequency response curves of the transimpedance amplifier of the present invention at different light intensities are shown. Detailed Implementation

[0038] The present invention will now be described in further detail with reference to the accompanying drawings and specific preferred embodiments.

[0039] In the description of this invention, it should be understood that the terms "left side," "right side," "upper part," "lower part," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. "First," "second," etc., do not indicate the importance of the components, and therefore should not be construed as a limitation of this invention. The specific dimensions used in this embodiment are only for illustrating the technical solution and do not limit the scope of protection of this invention.

[0040] like Figure 1As shown, a broadband transimpedance amplifier spike cancellation circuit includes a main amplification stage, a feedback network, and an automatic gain control circuit.

[0041] The main amplifier stage has an input terminal VI and an output terminal VO; the input terminal VI is used to receive the current signal from the external photodiode, and the output terminal VO is used to output the amplified voltage signal.

[0042] The main amplification stage mentioned above includes transistors Q1, Q2, and Q3, MOSFET M3, capacitor C1, and resistor R2.

[0043] The base of transistor Q1, the source of MOSFET M1, the lower plate of capacitor C2, the positive terminal of resistor R1, and the upper plate of capacitor C1 are all connected to the input terminal VI.

[0044] The upper plate of capacitor C1 is connected to the source of MOSFET M2; the drain of MOSFET M2 is connected to the negative terminal of inductor L2; the drain of MOSFET M1, the positive terminal of inductor L2, the collector of transistor Q1, and the emitter of transistor Q2 are connected; the base of transistor Q2 is connected to DC bias Vbcas.

[0045] The collector of transistor Q2, the negative terminal of resistor R2, the base of transistor Q3, and the output terminal VO are connected; the positive terminal of resistor R2 is connected to the collector of transistor Q3 and to the power supply; the emitter of transistor Q3, the collector of MOSFET M3, the negative terminal of resistor R1, and the lower plate of capacitor C1 are all connected to the negative input terminal of the automatic gain control circuit, which can reflect the intensity of the input optical signal; the gate of MOSFET M3 is connected to a fixed bias VBN and is used as a tail current source; the output terminal of the automatic gain control circuit is connected to the gates of MOSFETs M1 and M2.

[0046] Transistors Q1, Q2, and Q3 operate in the amplification region. MOSFET M3 is the tail current source operating in the saturation region.

[0047] The feedback network includes the feedback resistor R1 and the dynamically adjustable feedback network.

[0048] The feedback resistor R1 is the main feedback element, used to set the basic gain of the transimpedance amplifier.

[0049] The dynamic adjustment feedback network is connected in parallel with the feedback resistor R1, and includes the MOSFET M1 and the series resonant network.

[0050] The series resonant network consists of an inductor L2, a MOSFET M2, and a capacitor C2 connected in series.

[0051] The series resonant frequency of the aforementioned inductor L2 and capacitor C2 is configured to be the same as or close to the parasitic resonant frequency formed by the parasitic capacitance of the external photodiode and the inductance of the bond wire. The on-resistance of MOSFET M2 determines the quality factor Q of the series resonant network. The source of MOSFET M1 is connected to the input terminal VI, the drain of MOSFET M1 is connected to the positive terminal of inductor L2, the negative terminal of inductor L2 is connected to the drain of MOSFET M2, and the source of MOSFET M2 is connected to the input terminal VI via capacitor C2, thereby forming the dynamic adjustment feedback network.

[0052] The dimensions of the aforementioned MOSFET M2 are preferably selected such that the quality factor Q of the series resonant network matches the quality factor Q of the external parasitic resonant network where the external photodiode is located, thereby achieving the best peak elimination effect under different process and packaging conditions.

[0053] The aforementioned automatic gain control circuit can output a control voltage VFB based on the intensity of the input optical signal, dynamically adjusting the on-resistance of MOSFETs M1 and M2. Specifically, the automatic gain control circuit includes an error amplifier, whose positive input terminal is connected to a reference voltage Vref, its negative input terminal voltage is Vsense, and its output terminal generates the control voltage VFB after passing through a low-pass filter.

[0054] The aforementioned error amplifier can compare Vsense with Vref, thereby dynamically adjusting the transimpedance gain, specifically as follows:

[0055] When Vsense < Vref, the input optical signal is weak, and the control voltage VFB decreases, causing both MOSFETs M1 and M2 to be in the cutoff region. The feedback resistor R1 serves as the only feedback element. At this time, the current flowing through R1 is small, and the voltage at the negative input terminal of the circuit controlled by the automatic gain control circuit is high, while the VFB voltage is low. MOSFETs M1 and M2 operate in the cutoff region and exhibit a high configuration, with the transimpedance gain TZ = R1.

[0056] When Vsense≥Vref, the input optical signal is strong light, and the control voltage VFB increases, causing both MOSFETs M1 and M2 to operate in the linear region. The on-resistance of MOSFETs M1 and M2 is controlled by the control voltage VFB. The series resonant network is connected to the feedback path, generating a gain dip at the series resonant frequency of inductor L2 and capacitor C2, eliminating the frequency response spike caused by the parasitic resonance of the external photodiode.

[0057] When the input optical signal is strong light, the current flowing through R1 is relatively large. At this time, the voltage at the negative input terminal of the circuit controlled by the automatic gain control circuit is low, the VFB voltage is high, and MOSFETs M1 and M2 operate in the linear region. The expression for the transimpedance gain TZ is:

[0058]

[0059] In the formula, RM1 is the on-resistance of MOSFET M1, RM2 is the on-resistance of MOSFET M2, gm2 is the transconductance of transistor Q2, s is the complex frequency; C2 is the capacitance of capacitor C2; L2 is the inductance of inductor L2; R2 is the resistance of resistor R2; the symbol "||" indicates the parallel summation of the impedance values ​​before and after the symbol.

[0060] As can be seen from the above expression, the transimpedance is lowest at the resonant point of L2 and C2, and the relationship between the transimpedance gain and frequency is as follows: Figure 3 As shown. Compared to traditional transimpedance gain amplifiers, such as Figure 2 As shown, the transimpedance expressions for both are the same in low light conditions, while the transimpedance expression for a traditional transimpedance amplifier in high light conditions is:

[0061]

[0062] As can be seen from the expression, the frequency response curve of a traditional transimpedance amplifier under strong light is constant. Due to the parasitic capacitance and wire inductance of the photodiode, the cascaded circuit consisting of the photodiode and the transimpedance amplifier exhibits a spike in its frequency response curve, such as... Figure 4 As shown. Traditional transimpedance amplifiers cannot handle this spike, which manifests as a damped oscillation in the time domain, leading to a decrease in eye diagram quality and severely impacting bit error rate and communication quality. The resonant network in the broadband transimpedance amplifier spike cancellation circuit of this invention effectively eliminates the frequency response curve spike. The resonant frequencies of L2 and C2 are the same as the resonant frequencies of the parasitic capacitance and wire bonding inductance of the photodiode. Furthermore, the size selection of the MOSFET M2 is particularly important; since MOSFET M2 operates in the linear region, its on-resistance determines the Q value of the resonance between L2 and C2, and the resulting... Figure 3 The sharpness of the peak in the opposite direction. When the Q value of the resonant network formed by the parasitic capacitance and wire bonding inductance of the photodiode is high, a relatively sharp peak is generated in the band. Therefore, the size of MOSFET M2 needs to be increased accordingly to ensure that the resonant network of L2 and C2 has sufficient peak cancellation capability. Conversely, when the Q value of the resonant network formed by the parasitic capacitance and wire bonding inductance of the photodiode is low, a relatively gentle peak is generated in the band. Therefore, the size of MOSFET M2 needs to be decreased accordingly to ensure that the resonant network of L2 and C2 has corresponding peak cancellation capability. The frequency response curves of a conventional transimpedance amplifier and a broadband transimpedance amplifier peak cancellation circuit of the present invention under strong light are shown below. Figure 4 As shown, the frequency response curves of a conventional transimpedance amplifier and a broadband transimpedance amplifier spike cancellation circuit of the present invention at different light intensities are respectively shown in Figure 1. Figure 5 , Figure 6As shown in these two figures, the broadband transimpedance amplifier spike cancellation circuit of the present invention has better in-band flatness.

[0063] Furthermore, the broadband transimpedance amplifier spike cancellation circuit of the present invention is integrated into a single chip, and the input terminal VI is used to connect an external photodiode or avalanche photodiode.

[0064] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention, and these equivalent transformations all fall within the protection scope of the present invention.

Claims

1. A broadband transimpedance amplifier spike cancellation circuit, characterized in that: This includes the main amplifier stage, feedback network, and automatic gain control circuitry. The main amplifier stage has an input terminal VI and an output terminal VO; the input terminal VI is used to receive the current signal from the external photodiode, and the output terminal VO is used to output the amplified voltage signal. The feedback network includes the feedback resistor R1 and the dynamically adjustable feedback network; The feedback resistor R1 is the main feedback element, used to set the basic gain of the transimpedance amplifier; The dynamic adjustment feedback network is connected in parallel with the feedback resistor R1, and includes the MOSFET M1 and the series resonant network; The series resonant network consists of an inductor L2, a MOSFET M2, and a capacitor C2 connected in series. The automatic gain control circuit can output a control voltage VFB according to the intensity of the input optical signal, and dynamically adjust the on-resistance of MOSFETs M1 and M2.

2. The broadband transimpedance amplifier spike cancellation circuit according to claim 1, characterized in that: The series resonant frequency of inductor L2 and capacitor C2 is configured to be the same as or close to the parasitic resonant frequency formed by the parasitic capacitance of the external photodiode and the inductance of the bond wire, and the on-resistance of MOSFET M2 determines the quality factor Q of the series resonant network.

3. The broadband transimpedance amplifier spike cancellation circuit according to claim 1, characterized in that: The source of MOSFET M1 is connected to the input terminal VI, the drain of MOSFET M1 is connected to the positive terminal of inductor L2, the negative terminal of inductor L2 is connected to the drain of MOSFET M2, and the source of MOSFET M2 is connected to the input terminal VI via capacitor C2, thereby forming the dynamic adjustment feedback network.

4. The broadband transimpedance amplifier spike cancellation circuit according to claim 1, characterized in that: The main amplification stage includes transistors Q1, Q2, and Q3, MOSFET M3, capacitor C1, and resistor R2; The base of transistor Q1, the source of MOSFET M1, the lower plate of capacitor C2, the positive terminal of resistor R1, and the upper plate of capacitor C1 are all connected to the input terminal VI. The upper plate of capacitor C1 is connected to the source of MOSFET M2; the drain of MOSFET M2 is connected to the negative terminal of inductor L2; the drain of MOSFET M1, the positive terminal of inductor L2, the collector of transistor Q1, and the emitter of transistor Q2 are connected. The collector of transistor Q2, the negative terminal of resistor R2, the base of transistor Q3, and the output terminal VO are connected; the positive terminal of resistor R2 is connected to the collector of transistor Q3 and to the power supply; the emitter of transistor Q3, the collector of MOSFET M3, the negative terminal of resistor R1, and the lower plate of capacitor C1 are all connected to the negative input terminal of the automatic gain control circuit, which can reflect the intensity of the input optical signal; the gate of MOSFET M3 is connected to a fixed bias VBN and is used as a tail current source; the output terminal of the automatic gain control circuit is connected to the gates of MOSFETs M1 and M2.

5. The broadband transimpedance amplifier spike cancellation circuit according to claim 1 or 4, characterized in that: The automatic gain control circuit includes an error amplifier, whose positive input is connected to the reference voltage Vref, its negative input is Vsense, and its output is a control voltage VFB after passing through a low-pass filter.

6. The broadband transimpedance amplifier spike cancellation circuit according to claim 5, characterized in that: The error amplifier compares Vsense with Vref, thereby dynamically adjusting the transimpedance gain, specifically: When Vsense < Vref, the input optical signal is weak, the control voltage VFB decreases, so that both MOSFET M1 and MOSFET M2 are in the cutoff region, and the feedback resistor R1 is the only feedback element. At this time, the transimpedance gain TZ = R1. When Vsense≥Vref, the input optical signal is strong light, and the control voltage VFB increases, causing both MOSFETs M1 and M2 to operate in the linear region. The on-resistance of MOSFETs M1 and M2 is controlled by the control voltage VFB. The series resonant network is connected to the feedback path, generating a gain dip at the series resonant frequency of inductor L2 and capacitor C2, eliminating the frequency response spike caused by the parasitic resonance of the external photodiode.

7. The broadband transimpedance amplifier spike cancellation circuit according to claim 6, characterized in that: When the input optical signal is strong light, the expression for the transimpedance gain TZ is: ； In the formula, RM1 is the on-resistance of MOSFET M1, RM2 is the on-resistance of MOSFET M2, gm2 is the transconductance of transistor Q2, s is the complex frequency; C2 is the capacitance of capacitor C2; L2 is the inductance of inductor L2; R2 is the resistance of resistor R2; the symbol "||" indicates the parallel summation of the impedance values ​​before and after the symbol.

8. The broadband transimpedance amplifier spike cancellation circuit according to claim 1, characterized in that: The size of MOSFET M2 is selected such that the quality factor Q of the series resonant network matches the quality factor Q of the external parasitic resonant network where the external photodiode is located, thereby achieving the best peak elimination effect under different process and packaging conditions.

9. The broadband transimpedance amplifier spike cancellation circuit according to claim 1, characterized in that: The broadband transimpedance amplifier spike cancellation circuit is integrated into a single chip, and the input terminal VI is used to connect an external photodiode or avalanche photodiode.

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