A directly coupled ultra-wideband fixed-gain amplification module

Abstract

The present invention discloses a directly-coupled ultra-wideband fixed-gain amplification module, which divides a broadband signal into two paths: a high-frequency path and a low-frequency path. The low-frequency path is amplified by a common operational amplifier, while the high-frequency path is amplified by a low-noise broadband amplifier. After being amplified separately, the signals are combined. Among them, the high-frequency path adopts two-stage amplification, and an equalizer is used to compensate the high-frequency part between the two stages, so that the gain of the high-frequency signal remains flat within the entire frequency range of the high-frequency signal. At the same time, the low-frequency path adopts an adjustable low-pass filter (LPF) to adjust the flatness of the amplitude-frequency response of the overlapping band between the high-frequency path and the low-frequency path. In this way, the consistency of the low-frequency and high-frequency gains of the signal is ensured. The output signals of the high-frequency path and the low-frequency path are respectively input to the in-phase input terminal and the anti-phase input port of the differential driver, and a pair of differential signals that can be used to drive the ADC can be obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultra-wideband amplifiers. More specifically, it relates to a directly-coupled ultra-wideband fixed-gain amplification module applied to high-performance electronic test instruments. Background Art

[0002] The progress of technology has continuously promoted the development of the electronics industry. With the continuous improvement of circuit integration and production processes, the update cycle of electronic products is getting shorter and shorter, and both consumer and military electronic devices are accelerating their replacement. Behind the renovation of these devices, the support of various test instruments is indispensable. As the frequency of electronic signals increases, especially when the signal rise time decreases exponentially, higher requirements are put forward for broadband test instruments. Among them, amplifiers with higher bandwidths are important analog devices for signal integrity testing. For example, oscilloscopes, as a general test instrument, are widely used in the testing of various signals. Using oscilloscopes, tasks such as signal quality inspection, circuit fault diagnosis, power supply noise analysis, and eye diagram analysis can be completed. This requires the analog input bandwidth of the oscilloscope to cover from DC to GHz or even higher frequency ranges.

[0003] Principle of Ultra-wideband Amplifier:

[0004] Ultra-wideband amplifiers include types such as broadband operational amplifiers and low-noise amplifiers.

[0005] Broadband operational amplifiers achieve signal amplification through the principle of negative feedback. This method has good stability, but as the frequency increases, the delay of negative feedback becomes non-negligible, so the highest bandwidth is limited. Currently, known broadband operational amplifiers generally do not exceed 10 GHz, and the amplification factor is small, with weak amplification ability. They are usually used as broadband ADC drivers.

[0006] In the case of low-noise amplifiers (referred to as LNA for short), there are many broadband amplifiers that can achieve from low-frequency AC to high-frequency. However, due to the existence of input DC bias, the external input terminal must be input through a blocking capacitor, and it is impossible to amplify DC signals.

[0007] For broadband amplifiers from DC to higher bandwidths, foreign countries have adopted a customized integrated technology approach to solve the problem at the chip level, and the technology is strictly confidential, and the specific implementation principle is unknown. At present, China has less accumulation in this regard and needs to conduct research and exploration. Therefore, currently in China, discrete devices are generally used to build the analog front-end circuit, but the bandwidth and cost of discrete devices are often not ideal. The bandwidth of the analog channel is usually limited by the bandwidth of the amplifier, and it is difficult for ultra-wideband amplifiers to ensure the consistency of low-frequency and high-frequency gains, and their prices are often extremely expensive. Summary of the Invention

[0008] The object of the present invention is to overcome the deficiencies of the prior art and provide a directly-coupled ultra-wideband fixed-gain amplification module, so as to achieve ultra-wideband fixed-gain amplification while ensuring the consistency of low-frequency and high-frequency gains and having a relatively low price.

[0009] To achieve the above object of the invention, the directly-coupled ultra-wideband fixed-gain amplification module of the present invention is characterized in that it has a single-ended input and includes three parts: a high-frequency path, a low-frequency path, and a differential drive output. The broadband signal to be amplified is subjected to high-low frequency separation amplification by the high-frequency path for high-frequency signal amplification and the low-frequency path for low-frequency and DC signal amplification respectively, and then superimposed by a differential driver and output in a differential manner.

[0010] The high-frequency path includes a cascaded first-stage low-noise amplifier LNA1, an equalizer EQY, and a second-stage low-noise amplifier LNA2. After passing through the first-stage low-noise amplifier LNA1, the equalizer EQY, and the second-stage low-noise amplifier LNA2, the broadband signal serves as one input of the differential drive. Among them, the first-stage low-noise amplifier LNA1 and the second-stage low-noise amplifier LNA2 are used to amplify the high-frequency signal in the broadband signal, and the equalizer EQY plays a role of attenuation. Its high-frequency part has a small attenuation and compensates for the gain of the high-frequency parts of the first-stage low-noise amplifier LNA1 and the second-stage low-noise amplifier LNA2, so that the gain of the high-frequency signal remains flat within the frequency range of the entire high-frequency signal. The high-frequency signal amplified by the high-frequency path is output to the positive end of the differential driver.

[0011] The low-frequency path includes a cascaded adjustable low-pass filter LPF, a first-stage operational amplifier OPA1, and a second-stage operational amplifier OPA2. After passing through the adjustable low-pass filter LPF, the first-stage operational amplifier OPA1, and the second-stage operational amplifier OPA2, the broadband signal serves as the other input of the differential drive. Among them, the bandwidth of the adjustable low-pass filter LPF is adjustable and is used to adjust the flatness of the amplitude-frequency response of the overlapping band for high-low frequency separation between the high-frequency path and the low-frequency path. Among them, the first-stage operational amplifier OPA1 is a voltage follower, and the second-stage operational amplifier OPA2 is used for inverting amplification of the low-frequency signal. The amplification factor is the same as that of the high-frequency path and is a differential amplifier. One end of its input is connected to the output end of the first-stage operational amplifier OPA1, and the other end of the input is connected to a DC bias adjustment voltage for adjusting the DC bias. The low-frequency and DC signals amplified by the low-frequency path are output to the negative end of the differential driver.

[0012] Among them, the amplification factors, i.e., the gains, of the high-frequency path and the low-frequency path need to be kept consistent; the overlapping band for high-low frequency separation must be higher than the lower cut-off frequency of the first-stage low-noise amplifier LNA1 and the second-stage low-noise amplifier LNA2 and lower than the upper cut-off frequency of the first-stage operational amplifier OPA1 and the second-stage operational amplifier OPA2.

[0013] The object of the present invention is achieved in this way.

[0014] For the directly-coupled ultra-wideband fixed-gain amplification module of the present invention, in order to reduce costs, a low-noise amplifier broadband amplifier is used to build the amplification module. However, due to the influence of its internal structure and other reasons, the low-noise amplifier broadband amplifier cannot achieve direct coupling and cannot pass DC direct current or even low-frequency signals. Therefore, the present invention divides the broadband signal into two paths: a high-frequency path and a low-frequency path. The low-frequency path is amplified by an ordinary operational amplifier, while the high-frequency path is amplified by a low-noise amplifier broadband amplifier. After amplification respectively, the signals are combined. Among them, the high-frequency path adopts two-stage amplification, and an equalizer is used to compensate the high-frequency part between the two stages, so that the gain of the high-frequency signal remains flat within the entire frequency range of the high-frequency signal. At the same time, the low-frequency path adopts an adjustable low-pass filter LPF to adjust the flatness of the amplitude-frequency response of the overlapping band between the high-frequency path and the low-frequency path. In this way, the consistency of the low-frequency and high-frequency gains of the broadband signal is ensured. The output signals of the high-frequency path and the low-frequency path are respectively input to the in-phase input terminal and the anti-phase input terminal of the differential driver, and a pair of differential signals that can be used to drive the ADC can be obtained.

[0015] Based on the existing technology, the present invention has studied an ultra-wideband fixed-gain amplification module that can achieve direct current coupling and has a bandwidth of more than 10 GHz, solves the demand problem of the analog channel of existing test instruments (high-performance digital oscilloscopes) for broadband amplifiers, and can be used as a technical reference for further research on integrated broadband amplifiers. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic diagram of the principle of a specific embodiment of the directly-coupled ultra-wideband fixed-gain amplification module of the present invention;

[0017] Figure 2 is the circuit principle of a specific implementation of the directly-coupled ultra-wideband fixed-gain amplification module of the present invention;

[0018] Figure 3 is Figure 2 the equivalent input circuit of the directly-coupled ultra-wideband fixed-gain amplification module shown;

[0019] Figure 4 is Figure 2 the amplitude-frequency simulation result diagram of the directly-coupled ultra-wideband fixed-gain amplification module shown;

[0020] Figure 5 is Figure 2 the time-domain square wave response simulation diagram of the directly-coupled ultra-wideband fixed-gain amplification module shown. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] The specific embodiments of the present invention will be described below in conjunction with the accompanying drawings, so that those skilled in the art can better understand the present invention. It should be particularly noted that in the following description, when the detailed description of known functions and designs may dilute the main content of the present invention, these descriptions will be omitted here.

[0022] Due to the influence of its internal structure and other reasons, the LNA broadband amplifier cannot achieve direct coupling and cannot pass DC direct current or even low-frequency signals. Therefore, the present invention considers dividing the input amplified broadband signal into two paths, namely the high-frequency path and the low-frequency path. The low-frequency path can be amplified by an ordinary operational amplifier, while the high-frequency path is amplified by a low-noise amplifier, and the signals are combined after being amplified separately.

[0023] Usually, the input of a high-speed ADC is differential input. Therefore, the driving circuit of the high-speed ADC needs to adopt a differential structure output. The signals of the two paths can be input into the differential input of the driving circuit as a pair of "differential signals", and a pair of differential signals that can be used to drive the ADC can be obtained.

[0024] The present invention uses the existing broadband low-noise amplifier and low-frequency operational amplifier, adopts the method of separating the input broadband signal into high-frequency and low-frequency signals, and finally outputs the signals after superimposing through a differential driver. The principle composition is as Figure 1 shown.

[0025] Figure 1 It is a schematic diagram of the principle of a specific embodiment of the ultra-wideband fixed-gain amplification module with direct coupling of the present invention.

[0026] In this embodiment, as Figure 1 shown, the ultra-wideband fixed-gain amplification module with direct coupling of the present invention has a single-ended input, including three parts: a high-frequency path HF, a low-frequency path LF, and a differential drive output. The broadband signal to be amplified is separately amplified by the high-frequency path HF for high-frequency signal amplification and the low-frequency path LF for low-frequency and DC signal amplification through high-low frequency separation amplification, and then superimposed through a differential driver and output in a differential manner. Among them, the high-frequency path HF and the low-frequency path LF constitute a fixed-gain amplification.

[0027] The high-frequency path HF includes a cascaded first-stage low-noise amplifier LNA1, an equalizer EQY, and a second-stage low-noise amplifier LNA2. After the broadband signal passes through the first-stage low-noise amplifier LNA1, the equalizer EQY, and the second-stage low-noise amplifier LNA2, it serves as one input for differential driving. Among them, the first-stage low-noise amplifier LNA1 and the second-stage low-noise amplifier LNA2 are used to amplify the high-frequency signals in the broadband signal, and the equalizer EQY plays a role of attenuation. Its high-frequency part has a small attenuation and compensates for the gain of the high-frequency parts of the first-stage low-noise amplifier LNA1 and the second-stage low-noise amplifier LNA2, so that the gain of the high-frequency signal remains flat within the entire frequency range of the high-frequency signal. The amplified high-frequency signal of the high-frequency path is output to the positive end of the differential driver.

[0028] The low-frequency path LF includes a cascaded adjustable low-pass filter LPF, a first-stage operational amplifier OPA1, and a second-stage operational amplifier OPA2. After the broadband signal passes through the adjustable low-pass filter LPF, the first-stage operational amplifier OPA1, and the second-stage operational amplifier OPA2, it serves as the other input for differential driving. Among them, the bandwidth of the adjustable low-pass filter LPF is adjustable and is used to adjust the flatness of the amplitude-frequency response of the overlapping band between the high-frequency path HF and the low-frequency path LF. Among them, the first-stage operational amplifier OPA1 is a voltage follower. Among them, the first-stage operational amplifier OPA1 is a voltage follower, and the second-stage operational amplifier OPA2 is used for inverting amplification of the low-frequency signal. The amplification factor is the same as that of the high-frequency path and is a differential amplifier. One end of its input is connected to the output end of the first-stage operational amplifier OPA1, and the other end of the input is connected to the DC bias adjustment voltage for adjusting the DC bias. The amplified low-frequency and DC signals of the low-frequency path are output to the negative end of the differential driver.

[0029] Among them, the amplification factors, that is, the gains, of the high-frequency path HF and the low-frequency path LF need to be kept consistent; the overlapping band of high-low frequency separation must be higher than the lower cut-off frequency of the first-stage low-noise amplifier LNA1 and the second-stage low-noise amplifier LNA2, and lower than the upper cut-off frequency of the first-stage operational amplifier OPA1 and the second-stage operational amplifier OPA2.

[0030] The directly-coupled ultra-wideband fixed-gain amplification module of the present invention has a single-ended input. After high-low frequency separation and amplification, it is superimposed through differential driving and output in a differential manner. The high-frequency path HF includes two-stage low-noise amplifiers LNA1, LNA2, and an equalizer EQY. Among them, the low-noise amplifier is used to amplify the high-frequency signal, and the equalizer compensates for the high-frequency loss of the transmission path. The low-frequency path LF includes an adjustable low-pass filter LPF and two-stage operational amplifiers OPA1, OPA2. Among them, the bandwidth of the low-pass filter is adjustable and is used to adjust the flatness of the amplitude-frequency response of the overlapping band. OPA1 is a voltage follower, and OPA2 is used for amplification of the low-frequency signal. The amplification factor is the same as that of the high-frequency path, as well as the adjustment of the DC bias.

[0031] The directly coupled ultra-wideband fixed-gain amplification module of the present invention can perform ultra-wideband fixed-gain amplification. Its bandwidth and fixed-gain magnitude are mainly determined by the bandwidth and gain of the low-noise amplifier, and the amplification multiples of the two paths should be kept consistent, otherwise signal distortion will be caused. The present invention adopts direct-coupled input and can achieve the amplification of DC signals. The bandwidth of the low-noise amplifier on the current market can reach 10 kHz - 20 GHz. Therefore, the overlapping band of high-low frequency separation must be higher than the lower cut-off frequency of the first-stage low-noise amplifier LNA1 and the second-stage low-noise amplifier LNA2, and lower than the upper cut-off frequency of the first-stage operational amplifier OPA1 and the second-stage operational amplifier OPA2. The bandwidth of commonly used operational amplifiers can usually range from DC to several hundred MHz, which can meet the requirements.

[0032] In the high-frequency path HF of the present invention, the signal is amplified by cascading a low-noise amplifier and an equalizer. Usually, the fixed gain of the low-noise amplifier is about 14 dB, and the 6 dB equalizer has a 6 dB attenuation for signals with relatively low frequencies. To obtain a higher gain, two low-noise amplifiers are used. Therefore, it is calculated that the signal gain of the high-frequency path is 22 dB. The low-frequency path LF can adjust its gain to be the same as that of the high-frequency path by building the peripheral circuits of the first-stage operational amplifier OPA1 and the second-stage operational amplifier OPA2. Therefore, the gain of the signal is 22 dB.

[0033] The low-noise amplifier adopted in the present invention has the characteristics of low drift and low noise, and the OPA also has good low-frequency characteristics. Therefore, the overall module has the characteristics of low drift and low noise.

[0034] Specific implementation and verification

[0035] In this embodiment, the schematic diagram of the circuit principle of the specific implementation is as Figure 2 shown. This circuit realizes the functions of single-ended input and differential output, with an amplification multiple of about 22 dB and a DC input resistance of 50 ohms.

[0036] Among them, resistors R1, R2, R3, inductor L1, capacitor C1 and LNA1 constitute the input circuit, and the AC input resistance of the first-stage low-noise amplifier LNA1 in the subsequent stage is 50 Ω. The broadband signal passes through resistor R1 and inductor L1 to ground, and the series impedance is Z. The broadband signal is input to the first-stage low-noise amplifier LNA through capacitor C1. The resistance values of R2 and R3 are in the kΩ order of magnitude, which is much larger than 50 Ω and can be ignored. For the high-frequency signals in the broadband signal, this branch can be regarded as an open circuit. The adjustable resistor R4 and C2 constitute a low-pass filter LPF, which is used to adjust the flatness of the amplitude-frequency response of the overlapping band. The equivalent input circuit of the broadband gain module is as Figure 3 shown.

[0037] Figure 3In it, the dashed part is the equivalent input circuit of the low-noise amplifier LNA, and the resistance value of the low-noise AC equivalent input resistance R is 50 Ω. To satisfy the input resistance R i To be 50 Ω, the following conditions need to be met:

[0038]

[0039] Substitute R i = 50 Ω, and through calculation, it can be obtained that:

[0040]

[0041] That is:

[0042] Z == R + jR 2 wc (Equation 3)

[0043] Take R = 50 Ω to ensure that the low-frequency DC input resistance is 50 ohms, and take the inductor L1 = R 2 c, so Z can be expressed as a 50 Ω resistor R2 in series with the inductor L1, and the specific circuit corresponding to the impedance Z is as Figure 3 shown. Here, according to the actual situation, C = 0.01 uF and the inductor is 25 uH can be taken.

[0044] Due to the existence of the inductor, for high-frequency signals, the series connection of R1 and L1 can be regarded as an open circuit. Therefore, C1 and R form an RC high-pass filter, and its cut-off frequency is

[0045] f = 1 / 2∑RC (Equation 4)

[0046] According to different actual situations, different values of C1 can be selected to obtain different overlap bands. When changing C1, the inductance value of L1 needs to be adjusted to ensure that the input resistance always remains at 50 Ω. By selecting different resistors, adjusting the ratio of R6 to R5 and the voltage division of R2 and R3, the gain of the low-frequency path can be adjusted to be the same as that of the high-frequency. And by adjusting the adjustable resistor R4, the cut-off frequency of the LPF can be adjusted. Finally, the result with the flattest amplitude-frequency response can be obtained, and the obtained simulation result is as Figure 4 shown.

[0047] Judging from the simulation results, when the overlap band is controlled within several hundred KHz, the overall amplitude-frequency curve is relatively flat, which proves the feasibility of the fixed-gain module.

[0048] In addition to the amplitude-frequency response, the module conducts a time-domain analysis. Taking a 10 Hz square wave as the signal source, the waveform result obtained from the simulation is as Figure 5As shown. Among them, (a) is the time-domain characteristic curve of the input signal and the low-frequency path signal, (b) is the time-domain characteristic curve of the input signal and the high-frequency path signal, and (c) is the time-domain characteristic curve of the signal superposition output of the input signal of the fixed-gain module and the high and low frequency paths. From the simulation results, the overall flatness is good, which proves the feasibility of the fixed-gain module.

[0049] Summary:

[0050] The present invention uses an existing broadband high-performance low-noise amplifier to build an ultra-wideband fixed-gain amplification module capable of realizing DC direct coupling, provides a solution for realizing a directly coupled broadband gain amplifier, and has a low implementation cost and high performance-price ratio. It helps to improve the technical level of domestic high-performance digital oscilloscopes and has very good promotion value.

[0051] Although the above describes the illustrative specific embodiments of the present invention for the convenience of those skilled in the art to understand the present invention, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions created using the concept of the present invention are within the scope of protection.

Claims

1. A directly coupled ultra-wideband fixed-gain amplification module, characterized in that, It is a single-ended input, including three parts: a high-frequency path, a low-frequency path, and a differential drive output. The broadband signal to be amplified is subjected to high-low frequency separation amplification by the high-frequency path for high-frequency signal amplification and the low-frequency path for low-frequency and DC signal amplification respectively, and then superimposed by a differential driver and output in a differential manner; The high-frequency path includes a cascaded first-stage low-noise amplifier LNA1, an equalizer EQY, and a second-stage low-noise amplifier LNA2. The broadband signal passes through the first-stage low-noise amplifier LNA1, the equalizer EQY, and the second-stage low-noise amplifier LNA2 and serves as one input of the differential drive. Among them, the first-stage low-noise amplifier LNA1 and the second-stage low-noise amplifier LNA2 are used to amplify the high-frequency signal in the broadband signal. The equalizer EQY plays a role of attenuation. Its high-frequency part has a small attenuation and compensates for the gain of the high-frequency parts of the first-stage low-noise amplifier LNA1 and the second-stage low-noise amplifier LNA2, so that the gain of the high-frequency signal remains flat within the entire frequency range of the high-frequency signal. The high-frequency signal amplified by the high-frequency path is output to the positive end of the differential driver; The low-frequency path includes a cascaded adjustable low-pass filter LPF, a first-stage operational amplifier OPA1, and a second-stage operational amplifier OPA2. The broadband signal passes through the adjustable low-pass filter LPF, the first-stage operational amplifier OPA1, and the second-stage operational amplifier OPA2 and serves as the other input of the differential drive. Among them, the bandwidth of the adjustable low-pass filter LPF is adjustable and is used to adjust the flatness of the amplitude-frequency response of the overlapping band for high-low frequency separation between the high-frequency path and the low-frequency path. Among them, the first-stage operational amplifier OPA1 is a voltage follower, and the second-stage operational amplifier OPA2 is used for inverting amplification of the low-frequency signal. The amplification factor is the same as that of the high-frequency path and is a differential amplifier. Its input negative terminal is connected to the output terminal of the first-stage operational amplifier OPA1, and its input positive terminal is connected to the DC bias adjustment voltage for adjusting the DC bias. The low-frequency and DC signals amplified by the low-frequency path are output to the negative end of the differential driver; Among them, the amplification factors, that is, the gains, of the high-frequency path and the low-frequency path need to be kept consistent; the overlapping band for high-low frequency separation must be higher than the lower cut-off frequency of the first-stage low-noise amplifier LNA1 and the second-stage low-noise amplifier LNA2, and lower than the upper cut-off frequency of the first-stage operational amplifier OPA1 and the second-stage operational amplifier OPA2.

2. The directly-coupled ultra-wideband fixed-gain amplification module according to claim 1, wherein It also includes an input circuit. In the input circuit, the broadband signal passes through a resistor R1 and an inductor L1 to ground, and the series impedance is Z. The broadband signal is input to the first-stage low-noise amplifier LNA through a capacitor C1; By selecting different values of the capacitor C1, different overlapping bands can be obtained. When changing C1, the inductance value of the inductor L1 needs to be adjusted to ensure that the input resistance always remains at 50Ω.

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