CN201726369U - Radio-frequency power amplifier circuit with function of adjusting pre-distortion - Google Patents

Abstract

The utility model discloses a radio-frequency power amplifier circuit with the function of adjusting pre-distortion. The radio-frequency power amplifier circuit comprises a transistor with the structure of an emitter follower, wherein the base of the transistor is connected with the input end of the amplifier circuit; the emitter of the transistor is connected with the output end of the amplifier circuit through an output matching network; an RC parallel negative feedback network is connected between the base and the collector of the transistor; the collector of the transistor is connected with external adjustable bias voltage; a first RL series negative feedback network is also connected between the collector and the external adjustable bias voltage; and a second RL series negative feedback network is connected between the emitter of the transistor and the ground. The radio-frequency power amplifier circuit enables a pre-distortion circuit to have excellent accuracy and can compensate for gain compression and positive phase deviation generated by a post-stage circuit of the power amplifier, improve the linearity.

Description

Radio-frequency (RF) power amplifier circuit with adjustable predistortion function

Technical field

The utility model relates to a kind of radio-frequency (RF) power amplifier circuit with adjustable predistortion function.

Background technology

Power amplifier is one of the strongest non-linear device in the communication system, and the quality of the power amplifier linearity directly influences the performance of whole communication system.When the power amplifier input power is big, its active device parameter (transistor transconductance g _mAnd the junction capacitance C between base stage-collector electrode _μDeng) will change with input power, cause power amplifier to enter non-linear working state, produce gain compression (AM/AM) and this two quasi-nonlinears distortion of phase deviation (AM/PM).

At present, linearization technique commonly used in the circuit design mainly comprises: feedforward, feedback, predistortion, Digital Signal Processing predistortion and back are to distortion, and wherein pre-distortion technology is the simplest linearization technique the most commonly used.Adopt the circuit of pre-distortion technology can produce the predistortion of amplitude and phase place, thereby the nonlinear distortion of level generation behind the power amplifier is compensated in the power amplifier input stage.At present, two kinds of predistortion circuit structures commonly used are arranged: power absorption device and feedback network.These two kinds of structures all under fixing bias condition, just can be brought into play its predistortion function.The change of ambient temperature, the deviation of technology and transistorized wearing out all can cause the working point of circuit to change, and the compensation of this predistortion circuit was lost efficacy, thereby produce the nonlinear distortion that can not estimate.

Summary of the invention

The utility model purpose is: a kind of radio-frequency (RF) power amplifier circuit of adjustable predistortion function is provided, and it makes predistortion circuit have better accuracy, and the gain compression and the positive phase deviation that can the compensating power amplifier late-class circuit produce improve its linearity.

The technical solution of the utility model is: a kind of radio-frequency (RF) power amplifier circuit with adjustable predistortion function, the transistor that comprises the emitter follower structure, described transistorized base stage is connected with the input of amplifier circuit, described transistorized emitter-base bandgap grading is connected with the output of amplifier circuit by output matching network, from described transistorized base stage to being connected with RC negative feedback network in parallel the collector electrode, described transistorized collector electrode is connected with outside adjustable bias voltage, from described collector electrode to also being connected with RL series connection negative feedback network the outside adjustable bias voltage, from described transistorized emitter-base bandgap grading to being connected with the 2nd RL series connection negative feedback network the ground.

Wherein, described RC negative feedback network in parallel plays the effect of the input impedance, power gain and the positive phase skew that reduce circuit.Described RL series connection negative feedback network plays modulation RC negative feedback network feedback intensity in parallel.Described the 2nd RL series connection negative feedback network works to increase input impedance, power gain and the minus phase skew of circuit.By adjusting above-mentioned three negative feedback networks, get final product the size of control amplifier circuit power gain and the predistortion intensity of gain and phase place.By outside adjustable bias voltage externally the bias voltage of pair amplifier circuit finely tune, thereby the nonlinear distortion that can not estimate of generations such as compensate for ambient temperature change, process deviation and transistor ageing.

Further, in above-mentioned amplifier circuit, described negative feedback network in parallel comprises from transistorized base stage to first electric capacity of connecting the collector electrode and first resistance.

Further, in above-mentioned amplifier circuit, the described first series connection negative feedback network comprises from transistorized collector electrode to first inductance and second resistance of connecting the outside adjustable bias voltage.

Further, in above-mentioned amplifier circuit, the described second series connection negative feedback network comprises from transistorized emitter to second inductance of connecting the ground and the 3rd resistance.

The utility model has the advantages that:

1. the utility model to connecting RC negative feedback network in parallel between the collector electrode, has reduced the positive phase skew of predistortion circuit in the transistorized base stage of emitter follower structure.

2. the utility model to connecting RL series connection negative feedback network between the outside adjustable bias voltage, can be modulated the feedback intensity of RC in parallel negative feedback network by adjusting component value in the RL series connection negative feedback network at the transistorized collector electrode of emitter follower structure.

3. the utility model to being connected with the 2nd RL series connection negative feedback network between the ground, increases input impedance, power gain and the minus phase skew of predistortion circuit at the transistorized emitter of emitter follower structure.

4. the input of the utility model amplifier circuit can be directly matched to 50 ohm, need not extra matching network, is applicable to the design of wideband circuit.

5. the utility model externally is connected with adjustable bias voltage, by adjusting this bias voltage, and can the compensate for ambient temperature change, the nonlinear distortion that can not estimate of generation such as process deviation and transistor ageing.

Description of drawings

Below in conjunction with drawings and Examples the utility model is further described:

Fig. 1 a is the curve chart that the power gain of common power amplifier changes with input power;

Fig. 1 b is the curve chart that the phase deviation of common power amplifier changes with input power;

Fig. 2 is the circuit theory diagrams of the utility model specific embodiment;

Fig. 3 is the small-signal model equivalent circuit diagram of the utility model circuit theory diagrams.

The simulation curve figure that Fig. 4 a changes with input power for the gain of the utility model power amplifier;

Fig. 4 b is the simulation curve figure that the phase deviation of the utility model power amplifier changes with input power.

Wherein: 1RC negative feedback network in parallel; 2 the one RL negative feedback network of connecting; 3 the 2nd RL negative feedback network of connecting; 4 output matching networks; The IN input; The OUT output; The outside adjustable bias voltage of Vref; C1 first electric capacity; C2 second electric capacity; C3 the 3rd electric capacity; L1 first inductance; L2 second inductance; R1 first resistance; R2 second resistance; R3 the 3rd resistance; The Q1 transistor.

Embodiment

Embodiment:

Shown in Fig. 1 a and Fig. 1 b, the common power amplifier will be operated in nonlinear state along with the increase of input power in the prior art, produce the skew of gain compression and positive phase.Input power is big more, and it is non-linear serious more that power amplifier produces, and causes the gain compression amount big more, and the positive phase side-play amount is big more.

As shown in Figures 2 and 3, a kind of radio-frequency (RF) power amplifier circuit with adjustable predistortion function, the transistor Q1 that comprises the emitter follower structure, be that described transistor Q1 is a grounded-collector transistor, the base stage of described transistor Q1 is connected with the input IN of amplifier circuit, the emitter-base bandgap grading of described transistor Q1 is connected with the output OUT of amplifier circuit by output matching network 4, from the base stage of described transistor Q1 to being connected with RC negative feedback network 1 in parallel the collector electrode, from the collector electrode of described transistor Q1 to being connected with RL series connection negative feedback network 2 ground, from the emitter-base bandgap grading of described transistor Q1 to being connected with the 2nd RL series connection negative feedback network 3 ground.

Connect negative feedback network 2 to also being provided with outside adjustable bias voltage Vref the ground from a described RL.

Described RC negative feedback network 1 in parallel comprises that base stage from transistor Q1 is to first capacitor C 1 of connecting the collector electrode and first resistance R 1.

Described RL series connection negative feedback network 2 comprises that collector electrode from transistor Q1 is to first inductance L 1 and second resistance R 2 of connecting the outside adjustable bias voltage Vref.

Described the 2nd RL series connection negative feedback network 3 comprises that emitter from transistor Q1 is to second inductance L 2 of connecting the ground and the 3rd resistance R 3.

By adjusting connect with the 2nd RL component value in the negative feedback network 3 of RC negative feedback network 1 in parallel, RL series connection negative feedback network 2, the real part that makes the input impedance of grounded-collector transistor Q1 is 50 ohm, after the 3rd capacitor C 3 is connected, looking to grounded-collector transistor Q1 from signal input part presents 50 ohm of pure resistances, reaches to be directly matched to 50 ohm purpose.Make the circuit quiescent biasing in the saturation region, along with the increase of input power, bias point moves to the amplification region, the mutual conductance g among the grounded-collector transistor Q1 _mIncrease along with the increase of input power, the power gain of predistortion circuit also will increase thereupon, produce the power expansion.When input power further increases, the dynamic duty scope of grounded-collector transistor Q1 will enter degree of depth saturation region and cut-off region, cause its mutual conductance g _mMean value reduces, so the power gain of circuit will descend.Be externally connected to adjustable bias voltage Vref, by adjusting this bias voltage Vref, can the compensate for ambient temperature change, the nonlinear distortion that can not estimate of generation such as process deviation and transistor ageing.Externally adjustable bias voltage Vref connects the link of negative feedback network 2 to being connected with second capacitor C 2 between the ground with a RL, and AC signal is shorted to ground, eliminates the interference of AC signal to outside dc offset voltage Vref.

As shown in Figure 3, the small-signal model equivalent circuit diagram of the utility model circuit theory diagrams, wherein, g _m, C _π, C _μ, R _π, R _μBe respectively transistorized mutual conductance, emitter junction electric capacity, collector junction capacitance, emitter junction resistance, collector junction resistance, Z _InIt is the impedance of seeing into from the source end of signal input.

The input impedance of this circuit is:

$Z_{\mathrm{in}}=\frac{Z_{\mathrm{be}}-Z_E^{\′}+g_m{Z}_{\mathrm{be}}{Z}_E^{\′}}{1-A_i}---\left(1\right)$

Wherein

$A_i=-\frac{g_m{Z}_{\mathrm{be}}(Z_E^{\′}+Z_C)}{Z_{\mathrm{bc}}+Z_C}=-\frac{g_m{Z}_{\mathrm{be}}(Z_E^{\′}/Z_C+1)}{Z_{\mathrm{bc}}/Z_C+1}---\left(2\right)$

Z _E＝jwL _E+R _E

Z′ _E＝Z _E||R _L

Z _C＝jwL _C+R _C

$Z_{\mathrm{bc}}=(\frac{1}{\mathrm{jw}{C}_f}+R_f)\left|\right|\frac{1}{\mathrm{jw}{C}_{\mathrm{\μ}}}\left|\right|R_{\mathrm{\μ}}$

$Z_{\mathrm{be}}=R_{\mathrm{\π}}\left|\right|\frac{1}{\mathrm{jw}{C}_{\mathrm{\π}}}$

Power gain that can this predistortion circuit is:

$G_p=\frac{P_{\mathrm{out}}}{P_{\mathrm{in}}}\≈\frac{Z_{\mathrm{in}}}{Z_{\mathrm{in}}+R_S}\frac{Z_{\mathrm{in}}}{R_L}\≈\frac{1}{2}\frac{Z_{\mathrm{in}}}{R_L}---\left(3\right)$

By formula (3) as can be known, the power gain of this predistortion circuit is directly proportional with its input impedance.Analytically several formulas as can be known, RC negative feedback network 1 in parallel has reduced the input impedance and the power gain of this circuit, 3 of negative feedback networks of the 2nd RL series connection have increased the input impedance and the power gain of this circuit, the one RL series connection negative feedback network 2 has been modulated the feedback intensity of RC negative feedback network 1 in parallel, therefore by adjusting the size that above-mentioned three negative feedback networks 1,2,3 are this circuit power gain of may command and the predistortion intensity of gain and phase place.

Be depicted as the power gain of the utility model circuit theory diagrams and the simulation curve figure of phase deviation as Fig. 4 a and Fig. 4 b, predistortion amplifying circuit power gain is expanded along with the increase of input power, has expanded about 3dB at-2.2dBm input power point; The skew of its minus phase also increases along with the increase of input power, has increased about 3 ° at-13dBm input power point.Simultaneously, the size of external bias voltage Vref that can be by adjusting this predistortion circuit can change the degree of its gain expansion and phase deviation, realizes its controlled to late-class circuit nonlinear compensation intensity.

The utility model adopts the power gain and the phase deviation of series and parallel negative feedback network modulation circuit, by adjusting the external bias voltage of predistortion circuit, realizes the adjustable of its power gain expansion and phase deviation.With the input stage of this predistortion amplifying circuit as power amplifier, can compensate the gain compression and the phase distortion of late-class circuit effectively, significantly improve the linearity of power amplifier, and realized the external controllable of the linearity.

Claims (4)

1. radio-frequency (RF) power amplifier circuit with adjustable predistortion function, the transistor (Q1) that comprises the emitter follower structure, the base stage of described transistor (Q1) is connected with the input (IN) of amplifier circuit, the emitter-base bandgap grading of described transistor (Q1) is connected with the output (OUT) of amplifier circuit by output matching network (4), it is characterized in that: from the base stage of described transistor (Q1) to being connected with RC negative feedback network (1) in parallel the collector electrode, the collector electrode of described transistor (Q1) is connected with outside adjustable bias voltage (Vref), from described collector electrode to also being connected with RL series connection negative feedback network (2) the outside adjustable bias voltage (Vref), from the emitter-base bandgap grading of described transistor (Q1) to being connected with the 2nd RL series connection negative feedback network (3) the ground.

2. the radio-frequency (RF) power amplifier circuit with adjustable predistortion function according to claim 1 is characterized in that: described RC negative feedback network in parallel (1) comprises that base stage from transistor (Q1) is to first electric capacity (C1) of connecting the collector electrode and first resistance (R1).

3. the radio-frequency (RF) power amplifier circuit with adjustable predistortion function according to claim 1 is characterized in that: described RL series connection negative feedback network (2) comprises that collector electrode from transistor (Q1) is to first inductance (L1) and second resistance (R2) of connecting the outside adjustable bias voltage (Vref).

4. the radio-frequency (RF) power amplifier circuit with adjustable predistortion function according to claim 1 is characterized in that: described the 2nd RL series connection negative feedback network (3) comprises that emitter from transistor (Q1) is to second inductance (L2) of connecting the ground and the 3rd resistance (R3).

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