CN105243225A - Field effect transistor-based circuit design method for low noise source - Google Patents

Abstract

The invention provides a field effect transistor-based circuit design method for a low noise source. The circuit design method comprises the steps as follows: a drain side of a field effect transistor is connected to a terminal load from a low noise coefficient; a signal is output to an external system form a grid of the field effect transistor, so that a signal flow flows in from a drain and flows out from the grid as the direction; meanwhile, a conversion on impedance of system and terminal loads is carried out through designing input and output biases and a matching network, so that gamma<S> and gamma<L> required by an original element are displayed on the grid and the drain of the field effect transistor; and a signal with an extremely low noise temperature is obtained through a proper circuit design.

Description

A kind of circuit design method of the low noise sound source based on field effect transistor

Technical field

The invention belongs to microwave radio circuit engineering field, be specifically related to a kind of circuit design method of the low noise sound source based on field effect transistor.

Background technology

Field effect transistor, is a kind of voltage-controlled type unipolar transistor, has input resistance high by (10 ⁷~ 10 ¹⁵the advantages such as Ω), high-gain, noise are little, low in energy consumption, dynamic range large, be easy to integrated, do not have secondary-breakdown phenomenon, safety operation area field width.Along with the continuous progress of semiconductor technology, field effect transistor has now become the powerful rival of bipolar transistor and power transistor.All the time, the application mode of field effect transistor is mainly concentrated on utilize its high-gain characteristic Design amplifier.Be embodied in, using source electrode as common port, using grid as input stage, to drain as output stage, utilize the high-gain of field effect transistor, drain the signal of grid input after amplifying output certainly.In whole process, directions of signal flow is that grid enters, and drains out.According to above-mentioned principle, field effect transistor has been widely used in various types of amplifier, this application mode adopts forward signal stream, input signal after field effect transistor with about 10 times amplifications, obtaining powerful while, be also synchronously exaggerated noise, be unfavorable for that low noise exports, be namely conceived to the high gain characteristics of field effect transistor, and using its low-noise characteristic as secondary consideration, this seriously limits the range of application of field effect transistor in fact.

Summary of the invention

The object of the invention is to, for solving the confinement problems of field effect transistor application in prior art, the present invention proposes a kind of circuit design method of the low noise sound source based on field effect transistor.The starting point of the present invention is the another feature utilizing field effect transistor, i.e. low-noise factor.As the active device that current noise figure is minimum, some field effect transistor has the ultra-low noise coefficient being low to moderate 0.4dB, and the noise temperature of its correspondence is lower than 30K.At present, in fields such as microwave radiometries, the acquisition lower than the noise reference point of 290K is major issue, and the present invention starts with from low-noise factor, the drain electrode termination terminator of scene effect pipe, and obtains output signal from the grid of field effect transistor.Directions of signal flow to be gone out into grid for draining, completely contrary with traditional amplifier application mode.

The method is absorbed in the low-noise characteristic of field effect transistor completely, avoids field effect transistor enlarging function, thus can obtain extremely low noise power in gate terminal.Based on this kind of technology, can design with field effect transistor is the novel low-noise sound source of core, can be used for the device such as the cold load of noise measurement, the reference load of microwave radiometer, all significant to microwave radiometry, microwave noise benchmark, radio astronomy.

For achieving the above object, the circuit design method of a kind of low noise sound source based on field effect transistor provided by the invention, comprising:

Step 1) drain electrode of field effect transistor is connect terminator, and obtain from the grid of field effect transistor and output signal to external system, its grid is expressed as to the noise temperature of system orientation incidence:

T _S,1＝T _b+[(T ₁(1-|Γ _S| ²)+T _a)G ₂₁|Γ _L| ²+T ₂(1-|Γ _L| ²)]G ₁₂[K]

Wherein, T ₁the temperature of the system be connected with field effect transistor output terminal, T ₂for terminator temperature, G ₁₂and G ₂₁the power gain calculated by field effect transistor S parameter, Γ _sand Γ _lrepresent grid reflection coefficient and the drain electrode reflection coefficient of field effect transistor respectively, K represents Temperature Quantity unit Kelvin;

Step 2) according to the demand of noise temperature and the voltage output value of power module, select the bias point of field effect transistor, and inquire about field effect transistor at this biased lower scattering parameter and noise parameter, then emulate in the field effect transistor circuit model obtained substitution ADS microwave circuit simulation software;

Step 3) according to Γ _in=Γ _opt ^*power input matching condition, field effect transistor output port reflection coefficient calculate formula:

${\mathrm{\&Gamma;}}_L=\frac{{{\mathrm{\&Gamma;}}^{*}}_{opt}-S_{11}}{S_{12}{S}_{21}+S_{22}({{\mathrm{\&Gamma;}}^{*}}_{opt}-S_{11})}$

Calculate and obtain Γ _l, and by adjustment source inductance, until | Γ _l| reach minimum value, wherein S ₁₁, S ₁₂, S ₂₁, S ₂₂represent four parameters of S parameter matrix, Γ _inrepresent that self-field effect tube grid sees the reflection coefficient to noise source output terminal, Γ _opt ^*represent the optimum noise reflection coefficient under mismatched condition;

Step 4) design drain electrode matching network, to meet step 3) in | Γ _l| reach minimum value;

Step 5) design Gate matching network, make Γ _s=Γ _opt, Γ _optrepresent the optimum noise reflection coefficient under terminal matching condition.

As the further improvement of technique scheme, step 4) in design drain electrode matching network comprise: terminator chooses the resistive load of 50Ohm or 75Ohm, the drain impedance of described field effect transistor adopts the resistance reactance mating type of plural form, adopt T-shaped matching network, adopt discrete component or microstrip line mode to mate according to different requirement of engineering.

Through the design procedure of above method, gained circuit scene effect tube grid is with T _{s, 1}noise temperature externally systems radiate noise power, because field effect transistor has the noise figure lower than 1dB, circuit export noise temperature T _{s, 1}below 100K can be low to moderate.

The circuit design method advantage of a kind of low noise sound source based on field effect transistor of the present invention is:

One, the present invention first time use field effect transistor as noise source core, noise signal source before this, passive device is mainly core with noise resistance, active device mainly with gas-discharge tube, avalanche diode for core.

Two, present invention achieves the direct utilization to field effect transistor low-noise factor characteristic.Application in the past is all confined to using field effect transistor as Signal transmissions intermediary, and play amplification, and the present invention is using field effect transistor as signal generating source, direct output noise signal, this is that prior art is unexistent.

Three, field effect transistor signal source output noise temperature of the present invention is lower.All kinds of classical signal source, the minimum point of its noise temperature exported is subject to environment temperature restriction, and the signal source noise temperature under normal temperature must be the value higher than 290K, wants to obtain the noise temperature lower than room temperature, just needs cold-producing medium to reduce physical temperature.And utilize the noise source output noise temperature of method design of the present invention to be determined by the noise figure of microwave FET, adopt the field effect transistor of 0.4dB noise figure, Circuit theory can export the noise power being low to moderate 30K, this greatly reduces current obtainable noise low spot.

Four, noise measurement cold load, microwave radiometer reference load etc. are all kinds of requires responsive device to noise power to utilize the signal source of method design of the present invention to can be used in designing, all significant to microwave radiometry, microwave noise benchmark, radio astronomy.

Accompanying drawing explanation

Fig. 1 is the circuit topology figure of the low noise power microwave signal source based on field effect transistor.

Radio wave propagation block diagram when Fig. 2 is the low noise power microwave signal source circuit design based on field effect transistor.

Fig. 3 is circuit model and reflection wave principle corresponding relation schematic diagram.

Fig. 4 is | Γ _l| with T _{s, 1}the graph of a relation of minimum value.

Fig. 5 is the circuit design method process flow diagram of a kind of low noise sound source based on field effect transistor in the present invention.

Embodiment

Be described in detail below in conjunction with the circuit design method of drawings and Examples to a kind of low noise sound source based on field effect transistor of the present invention.

The circuit structure of the field effect transistor according to Fig. 1, relative to traditional field effect transistor as amplifier application, in practical circuit of the present invention, by reverse for field effect transistor use.Be embodied in, be originally used as the field effect transistor drain electrode termination of output stage resistive load and become terminating stage, and originally as the fet gate opening of input stage, outside output noise power.In the embodiment shown in fig. 1, field effect transistor adopts dual power supply mode to power, i.e. V _gand V _dhigh level is provided respectively to grid and drain electrode.Add direct current choke circuit and alternating current bypass electric capacity, direct current signal and AC signal are isolated.Capacitance is added, the feed-in of further isolated DC power before drain terminal load, after gate output terminal mouth.

In the content of invention, the microwave two-port network theoretical reflection set forth can provide signal by Fig. 2.In figure center section with the black box network description of S parameter matrix representation the wave propagation characteristic of two-port network, theoretical according to microwave engineering, we only need four parameters controlling S parameter matrix, get final product Complete Characterization two-port network, and without the need to knowing the inner concrete formation of black box, this theory is equally applicable to field effect transistor.The reflection coefficient of two ports four directions is altogether the then characterized signal transmission characteristics of two-port network.Wherein, Γ _sand Γ _inshow respectively and to be seen by system and see the reflection parameters to system to field effect transistor with by fet gate, and Γ _land Γ _outthen show respectively and see to field effect transistor by terminator and drained by field effect transistor and see reflection parameters to terminator.Microwave two-port network theoretical reflection has extracted unified parameter matrix and has characterized from the various microwave source device of numerous and complicated, enormously simplify the analytic process of microwave circuit.

Fig. 3 is circuit model and reflection wave principle corresponding relation schematic diagram, and this figure illustrates the method adopting two-port network theoretical reflection to carry out circuit design more intuitively.Circuit adopts common source form, and source terminal introduces perception feedback.The impedance network of grid and drain electrode end should play the effect regulating quiescent point, completes impedance matching again.According to optimum noise matching principle and power match principle, Γ should be had _s=Γ _opt, and Γ _swith Γ _lconjugation.

According to the theoretical reflection of two-port network, the field effect transistor of a drain electrode termination terminator, its grid to the noise temperature of system orientation incidence is:

T _S,1＝T _b+[(T ₁(1-|Γ _S| ²)+T _a)G ₂₁|Γ _L| ²+T ₂(1-|Γ _L| ²)]G ₁₂[K](1)

Wherein, T ₂for terminator temperature, T ₁it is the temperature of the system be connected with field effect transistor output terminal.G ₁₂and G ₂₁it is the power gain calculated by field effect transistor S parameter.Γ _sand Γ _lrepresent fet gate reflection coefficient and drain electrode reflection coefficient respectively, and T _a, T _bthen described by following two formulas:

$T_a=T_{e\left(\min \right)}+\frac{T_k{\left|{{\mathrm{\&Gamma;}}^{,}}_{opt}\right|}^2}{1-{\left|{{\mathrm{\&Gamma;}}^{,}}_{opt}\right|}^2}\&lsqb;K\&rsqb;---\left(2\right)$

$T_b=\frac{T_k}{1-{\left|{{\mathrm{\&Gamma;}}^{,}}_{opt}\right|}^2}-T_{e\left(\min \right)}\&lsqb;K\&rsqb;---\left(3\right)$

In formula, Temperature Quantity unit all adopts Kelvin (K), and reflection coefficient amount is all without unit.Wherein, T _{e (min)}=T ₀(NF _min-1), T _k=4T ₀r _ng _opt.And R _nand G _optbe respectively equivalent noise resistance and the optimum noise conductance of field effect transistor, T ₀for normal temperature condition, value 290K.

And Γ ^, _optbest reflection coefficient during field effect transistor drain electrode non-matching load of access, according to microwave electromagnetic field theory, Γ ^, _optwith the Γ under matched load condition _optpass be:

${{\mathrm{\&Gamma;}}^{,}}_{opt}=\frac{{{\mathrm{\&Gamma;}}^{*}}_{in}-{\mathrm{\&Gamma;}}_{opt}}{{\mathrm{\&Gamma;}}_{opt}{\mathrm{\&Gamma;}}_{in}-1}---\left(4\right)$

Wherein, Γ _inrepresent that self-field effect tube grid sees the reflection coefficient to noise source output terminal, Γ _optrepresent the optimum noise reflection coefficient under terminal matching condition

In circuit design process, be biased by design input and output and convert with the impedance of matching network to system and terminator, make it the grid of scene effect pipe and the Γ presenting original paper needs that drains _sand Γ _l.Again by suitable circuit design, T can be made _{s, 1}reach minimum, and physical circuit design cycle describes as follows.

First, according to microwave circuit optimum noise matching condition, design input matching network, makes Γ _s=Γ _opt.

Secondly, according to Γ _in=Γ _opt ^*power input matching condition, field effect transistor drain electrode end oral reflex coefficient must reach:

${\mathrm{\&Gamma;}}_L=\frac{{{\mathrm{\&Gamma;}}^{*}}_{opt}-S_{11}}{S_{12}{S}_{21}+S_{22}({{\mathrm{\&Gamma;}}^{*}}_{opt}-S_{11})}---\left(5\right)$

Wherein, Γ _opt ^*represent the optimum noise reflection coefficient under mismatched condition, S ₁₁, S ₁₂, S ₂₁, S ₂₂represent four parameters of S parameter matrix;

According to (4) formula, power input matching condition can cause Γ _opt ^,=0, this can be used for simplifying T _aand T _b, and then simplify (1) formula.

(1) formula after simplifying is asked | Γ _l| partial derivative, can obtain:

$\frac{\&part;T_{S,1}}{\&part;\left|{\mathrm{\&Gamma;}}_L\right|}=2G_{12}\{G_{21}\&lsqb;T_1(1-|{\mathrm{\&Gamma;}}_S{|}^2)+T_{e\left(\min \right)}\&rsqb;-T_2\}\left|{\mathrm{\&Gamma;}}_L\right|---\left(6\right)$

Now, by solving t after then can being simplified _{s, 1}time minimum | Γ _l|.When | Γ _l| → 0, have t _{s, 1}obtain extreme value.

Therefore, under optimum noise coupling and power input matching condition, T is solved _{s, 1}minimum problems be just converted into and solve | Γ _l| minimum value.Now, see that the reflection coefficient to field effect transistor has Γ _in=S ₁₁.

When | Γ _l| when=0, by the known Γ of power input matching condition _opt=S ₁₁ ^*, this then can by the S parameter realization regulating bias point or source impedance to show to change element.

In order to verify when power input matching condition requires | Γ _l| level off to 0 time T _{s, 1}there is minimum value, consider two of a pHEMT device independently bias points in embodiment, use AWR software emulation, adopt non-linear TOM3 model that Devices provides to organs weight.Scene effect pipe source electrode connects an ideal inductance, and its inductance value is variable.Device, source and load temperature are assumed to be 298K.Assuming that Input matching is in Γ _opt, and output reflection coefficient is provided to reach power input coupling by (5) formula.In formula that Fig. 4 indicates (5) | Γ _l| level off to 0 time T _{s, 1}there is minimum value.(and the adjustment of source inductance can change | Γ _l|)

As shown in Figure 5, according to the content of above-mentioned analysis, specific design step of the present invention can be done following summary:

Step 1) drain electrode of field effect transistor is connect terminator, and obtain from the grid of field effect transistor and output signal to external system, its grid is expressed as to the noise temperature of system orientation incidence:

T _S,1＝T _b+[(T ₁(1-|Γ _S| ²)+T _a)G ₂₁|Γ _L| ²+T ₂(1-|Γ _L| ²)]G ₁₂[K]

Wherein, T ₁the temperature of the system be connected with field effect transistor output terminal, T ₂for terminator temperature, G ₁₂and G ₂₁the power gain calculated by field effect transistor S parameter, Γ _sand Γ _lrepresent grid reflection coefficient and the drain electrode reflection coefficient of field effect transistor respectively, K represents Temperature Quantity unit Kelvin;

Step 2) according to the demand of actual task to noise temperature and the voltage output value of power module, select the bias point of field effect transistor, and according to scattering parameter under this is biased of the databook preliminary search field effect transistor of element manufacturer and noise parameter, then substituted in ADS microwave circuit simulation software by field effect transistor circuit model and emulate, the accuracy of verification msg handbook is also finely tuned;

Step 3) calculate Γ according to (5) formula under power match condition _lif, Γ _llittle not, then continue adjustment source inductance, until find | Γ _l| and T _{s, 1}minimum value, this process can adopt tuber function automatic operation in ADS simulation software, avoids the tedious work of manual adjustments;

Step 4) design drain electrode matching network, general, terminator chooses the resistive load of 50Ohm or 75Ohm, and the resistance reactance mating type of field effect transistor drain impedance necessarily plural form, traditional T-shaped matching network can be adopted, discrete component or microstrip line mode is adopted to mate, to reach 3 according to different requirement of engineering) the middle Γ calculated _l;

Step 5) design Gate matching network, make Γ _s=Γ _opt, in order to extensively be connected with multiple systems, output terminal also should be matched to international 50Ohm or 75Ohm.

For different bias point, above-mentioned steps can iterate, minimum to obtain | Γ _l| and T _{s, 1}.According to the field effect transistor noise source that above-mentioned steps designs, there is minimum noise power output.

It should be noted last that, above embodiment is only in order to illustrate technical scheme of the present invention and unrestricted.Although with reference to embodiment to invention has been detailed description, those of ordinary skill in the art is to be understood that, modify to technical scheme of the present invention or equivalent replacement, do not depart from the spirit and scope of technical solution of the present invention, it all should be encompassed in the middle of right of the present invention.

Claims (2)

1., based on a circuit design method for the low noise sound source of field effect transistor, it is characterized in that, comprising:

Step 1) drain electrode of field effect transistor is connect terminator, and obtain from the grid of field effect transistor and output signal to external system, its grid is expressed as to the noise temperature of system orientation incidence:

T _S,1＝T _b+[(T ₁(1-|Γ _S| ²)+T _a)G ₂₁|Γ _L| ²+T ₂(1-|Γ _L| ²)]G ₁₂[K]

Wherein, T ₁the temperature of the system be connected with field effect transistor output terminal, T ₂for terminator temperature, G ₁₂and G ₂₁the power gain calculated by field effect transistor S parameter, Γ _sand Γ _lrepresent grid reflection coefficient and the drain electrode reflection coefficient of field effect transistor respectively, K represents Temperature Quantity unit Kelvin;

Step 2) according to the demand of noise temperature and the voltage output value of power module, select the bias point of field effect transistor, and inquire about field effect transistor at this biased lower scattering parameter and noise parameter, then emulate in the field effect transistor circuit model obtained substitution ADS microwave circuit simulation software;

Step 3) according to Γ _in=Γ _opt ^*power input matching condition, field effect transistor output port reflection coefficient calculate formula:

${\mathrm{\&Gamma;}}_L=\frac{{{\mathrm{\&Gamma;}}^{*}}_{opt}-S_{11}}{S_{12}{S}_{21}+S_{22}({{\mathrm{\&Gamma;}}^{*}}_{opt}-S_{11})}$

Calculate and obtain Γ _l, and by adjustment source inductance, until | Γ _l| reach minimum value, wherein S ₁₁, S ₁₂, S ₂₁, S ₂₂represent four parameters of S parameter matrix, Γ _inrepresent that self-field effect tube grid sees the reflection coefficient to noise source output terminal, Γ _opt ^*represent the optimum noise reflection coefficient under mismatched condition;

Step 4) design drain electrode matching network, to meet step 3) in | Γ _l| reach minimum value;

Step 5) design Gate matching network, make Γ _s=Γ _opt, Γ _optrepresent the optimum noise reflection coefficient under terminal matching condition.

2. the circuit design method of the low noise sound source based on field effect transistor according to claim 1, it is characterized in that, step 4) in design drain electrode matching network comprise: terminator chooses the resistive load of 50Ohm or 75Ohm, the drain impedance of described field effect transistor adopts the resistance reactance mating type of plural form, adopt T-shaped matching network, adopt discrete component or microstrip line mode to mate according to different requirement of engineering.