CN108880483B - Broadband amplifier with noise feedforward cancellation - Google Patents
Broadband amplifier with noise feedforward cancellation Download PDFInfo
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- CN108880483B CN108880483B CN201810780790.8A CN201810780790A CN108880483B CN 108880483 B CN108880483 B CN 108880483B CN 201810780790 A CN201810780790 A CN 201810780790A CN 108880483 B CN108880483 B CN 108880483B
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
- H03F1/26—Modifications of amplifiers to reduce influence of noise generated by amplifying elements
Abstract
The invention provides a low-cost, miniaturized, high-gain and low-noise broadband radio frequency amplifier, which is characterized in that on the basis of a dual-channel feedforward noise cancellation structure, a first-stage output is connected to a grid electrode of a second-stage common-gate transistor to increase a channel, so that the overall gain of the amplifier can be greatly improved on the premise of ensuring noise cancellation. By an additional feed forward path the amplifier gain can be made above 20dB while the noise figure of the amplifier remains low due to noise cancellation. In addition, the amplifier can be completely composed of a transistor and a resistor, the manufacturing cost is extremely low, elements such as inductors which occupy relatively large packaging area are not adopted, and the miniaturization is realized.
Description
Technical Field
The invention relates to the field of signal processing, in particular to a noise feedforward cancellation broadband amplifier.
Background
An amplifier is an essential functional module for almost all rf transceiver systems. In analog cable (50-850MHz), digital satellite tv (950-. However, transistors and resistors bring large noise, which seriously affects the signal-to-noise ratio of the receiving system and reduces the sensitivity of the receiving system. In the case of amplifying a weak signal, the noise of the amplifier itself may interfere with the signal seriously, and it is desirable to reduce the noise to improve the signal-to-noise ratio of the output.
Fig. 1 illustrates a typical rf amplifier circuit in the prior art, which uses a gate series inductor, a source degeneration inductor, and a load capacitance-inductance resonant network to implement an amplifier with high gain and low noise figure, as shown. The inductor L1 can be tuned to the parasitic capacitance of the input transistor, and provides a certain passive voltage gain, thereby reducing the input equivalent noise; the inductor L2 is a source electrode attenuation inductor, and can greatly reduce the current noise of the transistor M1 while providing input matching; inductor L3 resonates with capacitor C2 to provide not only a high gain output impedance, but also an impedance transformation that transforms the internal high impedance to a reference impedance (typically 50 ohms) external to the module.
However, the above amplifier has the following disadvantages: firstly, the inductance-capacitance resonant network can provide a high-gain band-pass or band-stop function, but the bandwidth is narrow; secondly, the inductor occupies a large amount of internal area of the chip, and the cost is increased; finally, the narrow bandwidth results in some performance degradation due to some variation in all processes.
For the multimode receiver which is increasingly demanded at present, if a narrow-band low-noise amplifier is adopted, a plurality of narrow-band low-noise amplifiers are needed, and the consumed chip area is large. The progress of CMOS technology makes the design of wideband low noise amplifiers to meet the requirement of all signal reception in the ultra-wideband range, and suitable for multimode transceiver and software radio applications, but compared to narrowband low noise amplifiers, the noise performance of conventional wideband low noise amplifiers is far inferior to that of narrowband low noise amplifiers.
Therefore, a wideband amplifier with a sufficiently high power gain and a noise figure as low as possible, and with a volume as small as possible, is needed to meet the current requirements of rf processing.
Disclosure of Invention
The invention combines the noise cancellation and negative feedback channel technology, provides a circuit structure of a noise feedforward cancellation broadband low-noise amplifier, and realizes the advantages of wide working frequency band, low noise, miniaturization, low cost and the like of an amplifier circuit.
To achieve the object of the present invention, an embodiment of the present invention provides a noise feedforward cancellation wideband amplifier, characterized in that: the amplifier comprises a first current source, a second current source, transistors M1a, M1b, M2a, M2b and M3, a first capacitor, a first resistor and a second resistor;
the output end of the first current source is connected to the source of the transistor M1b, the gate of the transistor M1b is connected to the gate of the transistor M1a and the first end of the first resistor, and the connection node is used as a radio frequency input port; the drain of the transistor M1b is connected to the drain of the transistor M1a and the second end of the first resistor; the second end of the first resistor is also connected with the power supply voltage input end through a first capacitor and a second resistor which are sequentially connected in series; the drain of the transistor M3 is connected to the power supply voltage input terminal, the gate thereof is connected to the connection node of the first capacitor and the second resistor, and the source thereof is connected to the rf output port and the drain of the transistor M2 b; the output end of the second current source is connected to the drain of the transistor M2b, the gate of the transistor M2b is connected to the bias voltage, the source of the transistor M2b is connected to the drain of the transistor M2a, the gate of the transistor M2a is connected to the gate of the transistor M1a, and the source of the transistor M2a is grounded; and, the gate of the transistor M2b is connected to the connection point of the first capacitance and the second resistance via a coupling path;
the amplifier performs noise cancellation through a multipath noise feedforward path, thereby reducing the noise figure of the amplifier.
Further, the coupling path includes one of the following ways: directly, via a resistive connection, via a parallel resistive-capacitive connection, via a series inductive-capacitive connection, via an inductive connection.
Further, the transistor M2a is configured as a common source or a common emitter amplifier, and the transistor M2b is configured as a common gate amplifier or a common base amplifier.
Further, the first current source and the second current source adopt mirror current sources or current pumps, and the current sources are provided with overcurrent protection modules.
Furthermore, the radio frequency input port and the radio frequency output port are both connected with a grounded filter capacitor, and the source of the transistor M1b is connected with a grounded capacitor.
The scheme provided by the invention provides a low-cost, miniaturized, high-gain and low-noise broadband radio frequency amplifier, and the beneficial effects of the amplifier comprise that: (1) the transistor and the resistor can be completely formed, the manufacturing cost is extremely low, elements such as inductors and the like which occupy a packaging area are not adopted, and the miniaturization is realized; (2) on the basis of a double-channel feedforward noise cancellation structure, a channel is added by connecting the first-stage output to the grid of the second-stage common-gate transistor, and the overall gain of the amplifier can be greatly improved on the premise of ensuring noise cancellation. By an additional feed forward path the amplifier gain can be made above 20dB while the noise figure of the amplifier remains low due to noise cancellation.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Drawings
The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the example serve to explain the principles of the invention and not to limit the invention.
FIG. 1 is a circuit diagram of a typical RF amplifier of the prior art;
FIG. 2 is an amplifier circuit for dual-path noise feedforward cancellation according to an embodiment of the invention;
FIG. 3 is a schematic diagram of an amplifier circuit of the present invention;
fig. 4 is an improved three-path noise feed-forward cancellation amplifier circuit according to an embodiment of the present invention.
Detailed Description
To make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that the embodiments and features of the embodiments in the present application may be arbitrarily combined with each other without conflict.
As shown in fig. 2, a two-channel noise feedforward cancellation wideband amplifier circuit is shown. The amplifier is completely composed of a transistor and a resistor, and elements such as an inductor and the like which occupy relatively large area are not adopted. The transistors M1a, M1b and the resistor R form an amplifier a1, which provides a first-stage amplifier gain, the resistors R2 and C2 are inter-stage coupling circuits, the transistor M3 is a source follower circuit, which provides isolation and output matching of the first-stage amplifier to an output terminal OUT, and the transistors M2a and M2b form an amplifier a 2. Wherein A1 and M3 form a negative gain feedforward path, A1 and A2 form a positive gain feedforward path, and when two independent paths meet a certain condition, the current noises of M1a and M1b of the transistors can be completely cancelled out, so that the noise coefficient of the whole amplifier can be greatly reduced.
Specific principles as shown in fig. 3, gm, i represents the transconductance of transistors M1a and M1b whose current noise current will generate noise voltages Vx, n and Vy, n at nodes X and Y, respectively, so that the total output noise voltage is equal to:
Vout，n＝t1*In*(R+Rs+A*Rs)
where Vout, n is the total output noise voltage, t1 is a value between 0 and 1, In is the noise current of the transistor, Rs is the source impedance, generally equal to 50 ohms, and a is the gain of the amplifier In the above figure, it can be seen from the above equation that the output noise voltage is equal to zero when the amplifier gain satisfies the following equation:
A＝-(R+Rs)/Rs
the gain of the amplifier at this time is about (gm, M1a + gm, M1b) × R, gm, M1a and gm, M1b are the transconductance of transistors M1a and M1b, respectively.
Specifically, with reference to the actual amplifier circuit of fig. 2, a is gm, M2a/gm, M3, where gm, M2a, gm, and M3 are transconductance of the transistors M2a and M3, respectively, since the output needs to be matched to a reference 50 ohm, gm, M3 is 0.02S, since M2a and M3 have the same current, the transconductance is proportional to the current in a deep saturation region in consideration of the quadratic effect of the transistors, and the transconductance cannot be effectively increased by increasing the width-to-length ratio, the gain a is generally 4 to 5 at most, and assuming that a is-5, R is 4 Rs 200, since the gain of the first path is much larger than that of the second path, the overall gain of the amplifier is about (gm, M1a + gm, M1b), and is generally less than 20 dB.
The noise feedforward cancellation technology of the amplifier circuit fully utilizes two different channels (a negative gain feedforward path and a positive gain feedforward path), effectively eliminates current noise of an input transistor, and simultaneously achieves a high bandwidth/center frequency ratio. However, the above structure may face the following problems in use: since the gains of the two channels need to satisfy the condition of noise cancellation, when the condition is satisfied, the gain of the amplifier itself is limited to be relatively low, and under some receiving environments requiring high gain, the structure cannot satisfy both high gain and low noise.
In order to further make up for the above deficiencies, the invention introduces another noise elimination path, which can effectively reduce the equivalent input noise of the amplifier while ensuring high gain, thereby giving consideration to both high gain and low noise. FIG. 4 shows a further improved noise feed forward cancellation amplifier circuit in another embodiment of the invention: the transistors M4 and M5 and the bias current IBIAS1 form a mirror current source, the output end (the drain of M5) of the mirror current source is connected to the source of the transistor M1b, and the output end can be further connected with a grounded capacitor C1 for power filtering; the drain of the transistor M1b and the drain of the transistor M1a are connected to one end (terminal Y) of the resistor R; the gate of the transistor M1b is connected to the gate of the transistor M1a and the other end (terminal X) of the resistor R, and the connection node is used as the rf input port IN; the port IN may further be connected to a ground capacitor, preferably a parallel plate capacitor; the driving signal source Vs and the signal source resistor Rs input radio frequency signals into IN through a coupling capacitor; one end (end point Y) of the resistor R is also connected with a power supply voltage input end VCC through a capacitor C2 and a resistor R2 which are sequentially connected in series; the drain of the transistor M3 is connected to the power supply voltage input terminal VCC, the gate thereof is connected to the connection node (terminal a) of the capacitor C2 and the resistor R2, and the source thereof is connected to the rf output port OUT and the drain of the transistor M2 b; the radio frequency output port OUT can be further connected with a grounding capacitor, preferably a parallel plate capacitor; the transistors M6 and M7 and the bias current IBIAS2 form a mirror current source, and the output end of the mirror current source is connected to the drain electrode of the transistor M2 b; the gate of the transistor M2b is also connected to the required bias voltage source via an input resistor; the source of transistor M2b is connected to the drain of transistor M2a, the gate of transistor M2a is connected to the gate of transistor M1a, and the source of transistor M2a is connected to ground. The transistor M2a is configured as a common source or a common emitter amplifier tube; transistor M2b is configured as a cascode amplifier or a cascode amplifier.
Transistors M1a and M1b, and resistor R form amplifier a1, which provides the first stage amplifier gain, resistors R2 and C2 are inter-stage coupling circuits, transistor M3 is a source follower circuit, which provides isolation and output matching of the first stage amplifier to output terminal OUT, and transistors M2a and M2b form amplifier a 2; wherein A1 and M3 form a negative gain feed forward path and A1 and A2 form a positive gain feed forward path. Further, the gate of transistor M2B (terminal B) is coupled to terminal a to form an additional noise cancellation path in the form of, but not limited to: direct connection, through resistive connection, through a series resistive-capacitive connection, through a series inductive-capacitive connection, through an inductive connection, and the like.
Through the improvement, a path is added to the original amplifier from the output of the first stage to the gate of the common-gate transistor M2b of the second stage, so that the feedforward noise cancellation path specifically comprises: the first one is from the first stage output to the grid of M3 to the radio frequency output, and is negative gain; the second is that the first stage outputs to the grid of the transistor M2b and then to the radio frequency output, and the gain is positive; the third is that the rf input port goes directly to the gate of transistor M2a and then to the rf output, which is a negative gain. Although the gain of the amplifier as a whole is apparently reduced by adding the additional path, the condition for noise cancellation is satisfied by the following equation:
(R+Rs)(1+b)+A*Rs＝0
where b is the gain of the common-gate transistor M2b, b is a number between-1 and 0 due to the output impedance of M2a, so that a ═ R + Rs (1+ b)/Rs, assuming b ═ 0.5 and a ═ 5, then R ═ 9 ═ Rs 450 ohms, twice as much as the amplifier architecture shown in fig. 2. Although there are three paths, the gain is dominated by the first path, so the overall gain of the amplifier is (gm, m1a + gm, m1b) × R, assuming the input transconductance is unchanged, the gain of the amplifier of fig. 4 is 7-8 dB greater than the amplifier scheme of fig. 2. Thus, by selecting the appropriate size of M2b (the aspect ratio of the gate), a higher amplifier gain can be achieved based on satisfying the noise cancellation condition.
The laboratory simulation shows that: for the amplifier structure shown in fig. 2, when R is chosen to be much larger than Rs, although the gain is high, the noise cancellation condition is destroyed, so the noise figure is 1.5dB, very poor; however, when the noise cancellation structure shown in fig. 4 is introduced, which adds an additional feed-forward path, although the gain is reduced from 25dB to 20dB, the noise cancellation condition is satisfied, the noise figure is greatly reduced to 0.8dB, and the influence on the output matching is small. As can be seen from the data comparison, the noise cancellation structure of fig. 4 achieves higher amplifier gain than the amplifier structure of fig. 2 under the situation of achieving the same noise figure, and can achieve a gain above 20dB and a noise figure below 1dB at the same time.
The feed-forward dual-path noise cancellation structure of fig. 2 cannot satisfy both high gain and low noise in some reception environments requiring high gain (voltage gain exceeding 20dB is required in many applications) because the gains of the two paths satisfy the noise cancellation condition, and when the condition is satisfied, the gain of the amplifier itself is also limited to be low. The invention makes creative improvement, adds a new feed-forward path on the basis of the circuit structure of fig. 2, hardly changes indexes such as cost and power consumption of the circuit by connecting the first stage output to the grid of the second stage common grid transistor, but substantially changes the noise cancellation condition, thereby breaking the limitation of gain; when this condition is reestablished, a higher gain amplifier structure can be achieved while maintaining low noise characteristics.
Although the embodiments of the present invention have been described above, the above description is only for the convenience of understanding the present invention, and is not intended to limit the present invention. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (4)
1. A noise feed forward cancellation wideband amplifier, characterized by: the amplifier comprises a first current source, a second current source, transistors M1a, M1b, M2a, M2b and M3, a first capacitor, a first resistor and a second resistor;
the output end of the first current source is connected to the source of the transistor M1b, the gate of the transistor M1b is connected to the gate of the transistor M1a and the first end of the first resistor, and the connection node is used as a radio frequency input port; the drain of the transistor M1b is connected to the drain of the transistor M1a and the second end of the first resistor; the second end of the first resistor is also connected with the power supply voltage input end through a first capacitor and a second resistor which are sequentially connected in series; the drain electrode of the transistor M3 is connected with the power supply voltage input end, the grid electrode of the transistor M3 is connected to the connection node of the first capacitor and the second resistor, and the source electrode of the transistor M3 is connected to the radio frequency output port and the drain electrode of the transistor M2 b; the output end of the second current source is connected to the drain of the transistor M2b, the gate of the transistor M2b is connected to the bias voltage, the source of the transistor M2b is connected to the drain of the transistor M2a, the gate of the transistor M2a is connected to the gate of the transistor M1a, and the source of the transistor M2a is grounded; and, the gate of the transistor M2b is connected to the connection point of the first capacitance and the second resistance via a coupling path;
the amplifier reduces the noise figure of the amplifier by noise cancellation through a multipath noise feedforward path.
2. The wideband amplifier of claim 1, where the coupling path comprises one of: directly, via a resistive connection, via a parallel resistive-capacitive connection, via a series-connected inductive-capacitive connection, or via an inductive connection.
3. The wideband amplifier of claim 1 where transistor M2a is configured as a common source or cascode transistor and transistor M2b is configured as a common gate or common base amplifier transistor.
4. The wideband amplifier of claim 1, where the first current source and the second current source employ mirror current sources or current pumps.
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| CN110460312A (en) * | 2019-06-27 | 2019-11-15 | 天津大学 | A kind of low-noise amplifier of Broadband emission impedance stabilization |
| CN111245384A (en) * | 2020-01-16 | 2020-06-05 | 长沙瑞感电子科技有限公司 | Millimeter wave low noise amplifier and millimeter wave receiving circuit |
| CN112564635B (en) * | 2020-12-10 | 2023-03-21 | 广东工业大学 | LNA-oriented gain-increasing and noise-reducing circuit |
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