CN105305979A - Distributed amplifier circuit for perfecting linearity - Google Patents

Abstract

The invention discloses a distributed amplifier circuit for improving linearity, which comprises several gain units, an input on-chip inductor connected to the input end of each gain unit, an output on-chip inductance connected to the output end of each gain unit, and at least one of the An interstage matching capacitor is arranged before or after the input on-chip inductor, and a bias resistor is connected to the input end of each gain unit, and a bias voltage is applied from the other end of the bias resistor. The present invention can change the static operating point of each gain unit by adopting gain units with different circuit structures and applying different bias voltages, thereby improving their linearity. The devices are isolated, so that different bias voltages can be applied to the input terminals of each gain unit, thereby increasing the degree of freedom in design and debugging.

Description

A Distributed Amplifier Circuit with Improved Linearity

technical field

The invention belongs to the technical field of integrated circuits, in particular to a distributed amplifier circuit with improved linearity.

Background technique

The rapid development of wireless communication technology puts forward higher requirements on the data transmission rate and bandwidth of the communication system. Commonly used broadband amplifier design techniques include negative feedback, balanced amplifiers, resistor matching, and active matching, etc., but none of these techniques can effectively improve the gain-bandwidth product of the amplifier. Due to its structural characteristics, the distributed amplifier can break through the limitation of the gain-bandwidth product of the amplifier and realize wider-band signal amplification. a wide range of applications. Various types of structures have appeared in the current distributed amplifiers, including non-uniform structures, distribution-cascaded structures, etc., but they are all in the form of artificial transmission lines with low-pass structures. At this time, all gain units must work in the same In the bias state, the degree of design freedom is low, and it is impossible to improve the linearity and other performance of the distributed amplifier by setting different operating points.

The basic principle of the distributed amplifier is to form an artificial transmission line with the parasitic _capacitance of the transistor and the inductance element, so as to overcome the gain roll-off caused by the parasitic capacitance. The on-chip inductor L _Gi and the input impedance of the gain unit form the input artificial transmission line, and the on-chip inductor L _Di and the output impedance of the gain unit form the output artificial transmission line. Obviously, the input/output artificial transmission lines are all low-pass filter structures. In traditional distributed amplifiers, each gain unit must work under the same DC bias condition because the gain units at all levels are directly coupled.

Contents of the invention

In view of the above-mentioned deficiencies in the prior art, the present invention proposes a distributed amplifier circuit that improves linearity, and its technical solution is:

A distributed amplifier circuit for improving linearity, comprising several gain units and an input on-chip inductance connected to the input end of each gain unit, an output on-chip inductance connected to the output end of each gain unit, and at least one of the gain units An interstage matching capacitor is arranged before or after the input on-chip inductor, and a bias resistor is connected to the input end of each gain unit, and a bias voltage is applied from the other end of the bias resistor.

Preferably, an inter-stage matching capacitor is provided before each input on-chip inductor.

A coupling capacitor is respectively connected in series before the first output on-chip inductor and the last output on-chip inductor.

The gain unit is an NMOS transistor, the gate of which is an input terminal, and the drain is an output terminal.

The gain unit is composed of two connected NMOS transistors, the source of the first NMOS transistor is connected to the drain of the second NMOS transistor, the gate of the second NMOS transistor is an input terminal, and the drain of the first NMOS transistor is an output terminal.

The gain unit is composed of two NMOS transistors and an inductor, the source of the first NMOS transistor is connected to one end of the inductor, the other end of the inductor is connected to the drain of the second NMOS transistor, and the gate of the second NMOS transistor is The input terminal, the drain of the first NMOS transistor is the output terminal.

The present invention can change the static operating point of each gain unit by adopting gain units with different circuit structures and applying different bias voltages, thereby improving their linearity. The devices are isolated, so that different bias voltages can be applied to the input terminals of each gain unit, thereby increasing the degree of freedom in design and debugging.

Description of drawings

Fig. 1 is a traditional distributed amplifier circuit structure diagram;

Fig. 2 is a circuit structure diagram of a distributed amplifier according to an embodiment of the present invention;

Fig. 3 is a structural diagram of an embodiment of the gain unit in Fig. 2;

FIG. 4 is a structural diagram of another embodiment of the gain unit in FIG. 2;

FIG. 5 is a structural diagram of another embodiment of the gain unit in FIG. 2;

Fig. 6 is the relation of output current, transconductance gain and each order derivative and input voltage of Fig. 3 embodiment;

FIG. 7 shows the relationship between the output current, transconductance gain and derivatives of each order and the input voltage of the embodiment shown in FIG. 4 and FIG. 5 .

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

The distributed amplifier circuit structure of the present invention is shown in Figure 2, compared with the traditional distributed amplifier shown in Figure 1, there are the following three improvements:

(1) There is an interstage matching capacitor before or after at least one input on-chip inductor, which forms a bandpass matching network with L _Gi . In Figure 2, a capacitor C _Gi is connected before each input on-chip inductor L _Gi . In fact, C _Gi can also be placed after L _Gi ; the number of C _Gi is [1,N];

(2) An independent bias structure R _Gi is adopted at the input end of the gain unit provided with an inter-stage matching capacitor, so that different bias voltages V _Gi can be applied to the input end of the gain unit;

(3) The gain unit can adopt any circuit structure as shown in Fig. 3 to Fig. 5, but the same circuit structure is generally adopted in the same circuit.

The principle of the distributed amplifier circuit of the present invention is as follows:

There is always the following relationship between the output current i _o of the gain unit and the input bias voltage v _in

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; g</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; g</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}^{<span\; class="notranslate">\; \&prime;</span>}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; g</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}^{<span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; \&prime;</span>}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}$

Where g _m represents the transconductance gain of the gain unit, g′ _m is the second derivative of i _o with respect to v _in , and g″ _m is the third derivative of i _o with respect to v _in .

According to the theory of radio frequency circuits, g″ _m has the greatest influence on the linearity performance of the amplifier. When g _m is constant, the smaller g″ _m is, the better the linearity of the amplifier is. The relationship between the transconductance characteristics and the input bias voltage of gain units with different structures is shown in Figure 6 and Figure 7 .

As shown in Figure 3, one structure of the gain unit is an NMOS transistor, the gate of which is the input terminal, and the drain is the output terminal. The distributed amplifier circuit with this structure outputs current, transconductance gain and derivatives of each order and input voltage The relationship is shown in Figure 6. It can be seen from Figure 6(b) that the gain unit presents serious nonlinearity, that is, the transconductance gain g _m is not a constant value, but changes with the input bias voltage v _in , so when the input signal of the amplifier As the amplitude increases, the output signal will appear nonlinearly distorted.

As shown in Figure 4, another structure of the gain unit is: the gain unit is composed of two connected NMOS transistors, the source of the first NMOS transistor is connected to the drain of the second NMOS transistor, and the gate of the second NMOS transistor is The input terminal, the drain of the first NMOS transistor is the output terminal.

As shown in Figure 5, another structure of the gain unit is: the gain unit is composed of two NMOS transistors and an inductor, the source of the first NMOS transistor is connected to one end of the inductor, and the other end of the inductor is connected to the drain of the second NMOS transistor pole, the gate of the second NMOS transistor is the input terminal, the drain of the first NMOS transistor is the output terminal, and the inductance is the peak inductance. Figure 7 shows the relationship between the output current, transconductance gain and each order derivative of the distributed amplifier circuit with the two structures shown in Figure 4 and Figure 5, and the input voltage. It can also be seen from Figure 7(a)(b) that the gain unit presents serious nonlinearity, that is, the transconductance gain g _m is not a constant value, but changes with the input bias voltage v _in , so when When the input signal amplitude of the amplifier increases, the output signal will appear non-linear distortion.

According to the working principle of the distributed amplifier, its forward transconductance gain is the superposition of the transconductance gains of each gain unit, so it can be seen from Figure 6(d) and Figure 7(d) that when each gain unit adopts the same (or different ) circuit structure and at different input bias voltages, g″ _m can take positive or negative values, so it is only necessary to adjust the bias voltage of each gain unit to make the total transconductance of the distributed amplifier The second-order partial derivative of the gain approaches zero, resulting in good linearity.

The technical means disclosed in the solutions of the present invention are not limited to the technical means disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features.

Claims (6)

1. A distributed amplifier circuit for improving linearity, comprising several gain units and an input on-chip inductance connected to each of the gain unit input terminals, an output on-chip inductance connected to each of the gain unit output terminals, characterized in that An interstage matching capacitor is provided before or after at least one input on-chip inductor, a bias resistor is connected to the input end of each gain unit, and a bias voltage is applied from the other end of the bias resistor. 2. The distributed amplifier circuit according to claim 1, wherein an interstage matching capacitor is provided before each input on-chip inductor. 3. The distributed amplifier circuit according to claim 1, wherein a coupling capacitor is connected in series before the first output on-chip inductor and the last output on-chip inductor respectively. 4. The distributed amplifier circuit according to claim 1, wherein the gain unit is an NMOS transistor, the gate of which is an input terminal, and the drain is an output terminal. 5. The distributed amplifier circuit according to claim 1, wherein the gain unit is composed of two connected NMOS transistors, the source of the first NMOS transistor is connected to the drain of the second NMOS transistor, and the second NMOS transistor is connected to the drain of the second NMOS transistor. The gate of the NMOS transistor is an input end, and the drain of the first NMOS transistor is an output end. 6. The distributed amplifier circuit according to claim 1, wherein the gain unit is composed of two NMOS transistors and an inductor, the source of the first NMOS transistor is connected to one end of the inductor, and the inductor's The other end is connected to the drain of the second NMOS transistor, the gate of the second NMOS transistor is an input end, and the drain of the first NMOS transistor is an output end.