CN1196615A

CN1196615A - Broadboard low-noise low intermodulation distortion receiver

Info

Publication number: CN1196615A
Application number: CN 97103771
Authority: CN
Inventors: 庄睛光; 林镇华; 林赞西
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-04-11
Filing date: 1997-04-11
Publication date: 1998-10-21
Anticipated expiration: 2017-04-11
Also published as: CN1069007C

Abstract

An integrated receiver with broad bandwidth, low noise and low intermodulation distortion features it is suitable for very wide RF range and has low noise coefficient, low intermodulation distortion, fixed input impedence in wide frequency range, stable signals and low energy radiation, so it can be integrated in very small crystal element area.

Description

Broadboard low-noise low intermodulation distortion receiver

The present invention is about a kind of broad-band receiver, particularly a kind of monocrystalline integrated circuit receiver that is applicable to very wide radio frequency signal frequency scope.

Along with being extensive use of of high frequency communication system, the demand of high-quality broad-band receiver grows with each passing day, and traditional receiver such as TV tuner can't satisfy the demands gradually fully.In addition,, use the design of discrete elements before, also, the substitute is radio frequency monocrystalline integrated circuit broad-band receiver because of volume can't use too greatly in conjunction with the PC tuner.

It is in above-mentioned reason, and the receiver of many use integrated circuit (IC) design arises at the historic moment.Figure 1A is the design of a typical TV/VCR receiver, whole receiver circuit comprises: UHF input filter 20, VHF input filter 21, two low noise radio frequency amplifiers 22 and 2.3, two intergrade filtering 24 and 25, arsenic potassium tuner integrated circuit 26, vibration resonant tank 27, intermediate-frequency filter 28, the peripheral loop 29 of intermediate frequency amplifier and divider 30 etc.This receiver utilizes two different filter circuit 20,21 and differential type low noise amplifiers 22,23 earlier, cooperate Bu and two wave band control signals of Bv, amplified respectively after radiofrequency signal is divided into VHF/CATV and two kinds of signals of UHF, import different intergrade filter circuit 24,25 then to finish an action of tracking filtering else, two signals after the processing import respectively in the tuner integrated circuit 26 again.Figure 1B is the inside calcspar of tuner integrated circuit 26, comprising: wave band diverter switch 261, UHF wave band with oscillator 262, VHF/CATV wave band with oscillator 263, vibration output buffer 264, bidirectional balanced formula modulator 265, and loop such as intermediate frequency amplifier 266.Two signals that import this integrated circuit 26 are introduced into wave band diverter switch 261, with the Bv control signal select be by the VHF/CATV band signal or by the UHF band signal by entering modulator 265.In addition, use the Bu control signal to switch the resonant tank that uses the outer corresponding wave band of integrated circuit.The channel lock out action then cooperates phase-locked loop controller (not being shown on the figure) to finish for divider 30 (Fig. 1) by oscillator output signal.To import the modulator hybrid modulation through the radiofrequency signal and the local oscillated signal of suitable switching output, the intermediate frequency amplifier 29 that imports again in the integrated circuit after the intermediate-frequency filter 28 of its output outside integrated circuit 26 detects amplifies, and its final intermediate frequency output enlargement ratio is then controlled by another U/V gain control signal Bm.Though this receiver has used radio frequency integrated circuit design, but because the electrical characteristic of this integrated circuit is unsatisfactory, special as the noise coefficient greater than 8dB, need outside integrated circuit, increase many discrete elements loop and improve, so UHF high frequency band characteristic is caused not unrestrained influence.

Fig. 2 A is a satellite television tuned receiver, and its suitable and radio frequency signal frequency scope is from 950MHz to 2GHz.Whole system is except a radio frequency integrated circuit 40, and peripheral circuit only has one group of resonant tank 41 and several coupling capacitance CA and CB, forms very simple.This integrated circuit 40 is made up of radio frequency amplifier RFAMP, smear modulator MIX, local oscillator OSC and intermediate frequency amplifier IFAMP.The middle frequency input terminal IF of this integrated circuit 40 should have an intermediate-frequency filter to be connected in this place (not showing among Fig. 2 A).

This integrated circuit uses special hoist type GaAs metal-semiconductor field effect transistor processing procedure, is different from general vague and general type processing procedure commonly used; In addition, the greatest feature of circuit shown in Fig. 2 A is the multidirectional oscillatory type oscillator that uses shown in Fig. 2 B, cooperate suitable external resonant tank, can in quite wide frequency range, obtain negative resistance property, show that it is good wide band oscillate, in addition because it is output as differential type, so can directly import bidirectional balanced modulator.

Though this receiver simple structure, its noise coefficient are greater than 10dB and only be suitable for satellite TV channel, can't be applied to general wired or wireless TV, practicality is subjected to very big restriction.

Fig. 3 shows a kind of integrated tuner system that is applicable to cable TV (CATV).This system adopts the twice frequency conversion structure, after using the processing and amplifying of radiofrequency signal through the low noise automatic gain control amplifier 501 in the integrated circuit of a femaleization gallium upconverter integrated circuit 50 earlier with the 50-550MHz of input, the mixer 502 that the output of first local oscillator 503 in integrated circuit imports in the integrated circuit is done the smear modulation treatment, again its output is imported the first outer intermediate-frequency filter 51 of integrated circuit, detect first intermediate-freuqncy signal (as 700MHz) after the up-conversion, this signal imports the second outer mixer 52 of integrated circuit with outer second local oscillations, 53 outputs of integrated circuit again and does modulation, and its output imports the 45MHz intermediate-freuqncy signal after second intermediate-frequency filter detects down converted.After the foregoing circuit processing, whole system roughly can also satisfy the electrical specification of CATV tuner.But this design is only applicable to the frequency range 50-550MHz of CATV.In addition, owing to use transistorized linear work district to do automatic gain control, the signal strength range that can modulate is very little, is fixed with adverse influence for the magnification distortion of big radiofrequency signal and the intensity of intermediate frequency output.In addition, owing to use twice frequency conversion mechanism, and only integrated freq converting circuit for the first time in the integrated circuit must expend more outward element to finish frequency translation function for the second time, can't simplify system's structure dress.

In sum, known receiver still has many always waiting to improve: at first, receiver is suitable for frequency range and remains to be increased, otherwise can't expand its application; The reduced phase noise of the electrical characteristic of receiver itself such as low noise coefficient, good linearity of amplifier degree, low intermodulation distortion and oscillator must be improved especially, in the hope of satisfying the more high-quality requirement of high image quality digital television receiver; Moreover, in order to design carry-along micro-receiver, have to use the monocrystalline radio frequency integrated circuit to replace most discrete elements design, and integrated circuit external circuits number must drop to minimum; At last, using simple and ripe integrated circuit manufacture process also is the task of can not ignore to reduce production costs.

Based on above requirement, the present invention proposes a kind of low intermodulation distortion broad-band receiver of whole differential low noise of integrability, and its characteristic is comprehensively as follows:

(1) is suitable for very wide radio frequency signal frequency scope, can contain cable TV 50 to 550MHz, the 950MHz of 50 to 900MHz and satellite television of VHF/UHF radiovision is to 2GHz even higher frequency application (looking the technology of microwave integrated circuit processing procedure, applicable to for example 5GHz).

(2) realize following function in above-mentioned frequency range:

(a) less than the low noise coefficient of 6dB:

(b) low intermodulation distortion, when the specified channel signal strength signal intensity was 60dB μ V, non-specified channel signal strength signal intensity must could cause 1% intermodulation distortion rate greater than more than the 95dB μ V on intermediate-freuqncy signal;

(c) the input impedance value is almost fixing (representative value is 75 Ω or 50 Ω);

(3) whole system employing differential type loop design, all high-frequency signals all with two coupling cablings, are not subject to the unsteady interference in zero potential ground, system stability.In addition, because two positive and negative two end signals of coupling line are combined closely, the less radiation of energy leaks outside, and is easy to by the electromagnetic field safety verification;

(4) all adopt active member direct-current coupling between each circuit of system kernel heart part, can be integrated into the very little integrated circuit of brilliant elemental area easily, add its periphery and cooperate circuit few, can be designed to high-quality micro-receiver system easily.

Broadboard low-noise low intermodulation distortion receiver of the present invention, comprise: the differential type low noise amplifier, receive the differential type of input or single-ended radio frequency signal and with its amplification, have the low magnification distortion characteristic of low noise coefficient and large-signal, and finish input impedance matching and the function of exporting differential wave; First buffer receives the output signal of this differential type low noise amplifier, has Dc bias adjustment, output buffering and functions such as adverse current prevents; First converter receives the output signal of this first buffer, will cause the large amplitude voltage signal of serious signal magnification distortion to convert relative amplitude less current signal linearly to; Automatic gain control amplifier, receive the current signal that this first converter is exported, and utilize intermediate frequency output amplitude transducer to tap into amplification or reduction magnification that next gain control signal is adjusted amplifier, make the amplitude of its output signal keep fixed size; Second buffer receives the output signal of this automatic gain control amplifier, is same as this first buffer and also has Dc bias adjustment, output buffering and functions such as adverse current prevents; Tracking filter receives the output signal of this second buffer, and according to the control signal of input the radiofrequency signal of assigned frequency is passed through, and other signals are filtered; Second converter receives the radiofrequency signal with assigned frequency that this tracking filter is exported, and converts the large amplitude voltage signal to relative amplitude less current signal linearly; The voltage controlled oscillator core, resonator, second buffer and phase-locked loop controller, four constitute a complete phase locked loop system jointly, its annexation receives the control signal of this phase-locked loop controller with the decision frequency of oscillation for this resonator, this voltage controlled oscillator core is connected in this resonator, to have the signal of this frequency of oscillation and shake, this signal that shakes enters this phase-locked loop controller through the 3rd buffer more then, this second buffer similarly has the Dc bias adjustment, output buffering and functions such as adverse current prevents, this phase-locked loop controller receiving channels data command and to export the wave band control signal used with frequency trim signal this resonator of confession and this tracking filter; Modulator receive two groups of signals from this second converter and the 3rd buffer, and output signal is the product of these two groups of signals; The 4th buffer receives the output signal of this modulator, has Dc bias adjustment, output buffering and functions such as adverse current prevents equally; Intermediate-frequency filter receives the output signal of the 4th buffer, in order to detect the usefulness of final intermediate-freuqncy signal for signal demodulation thereafter.

In addition, Broadboard low-noise low intermodulation distortion receiver of the present invention also comprises: preposition selective filter, the differential type or the single-ended radio frequency signal of input enter before the differential type low noise amplifier, be introduced into this preposition selective filter, in order near the signal the initial option specified channel, and optionally finish the function of impedance transformation.

Figure 1A is the design of the TV/VCR receiver of a known techniques;

Figure 1B is the inside calcspar of tuner integrated circuit 26 in the receiver shown in Figure 1A;

Fig. 2 A is the design of the satellite television tuned receiver of a known techniques;

Fig. 2 B is and the employed multidirectional oscillatory type oscillator of the receiver of Fig. 2 A;

Fig. 3 is the integrated tuner system that is applicable to cable TV of a known techniques;

Fig. 4 A is the calcspar of Broadboard low-noise low intermodulation distortion receiver of the present invention;

Fig. 4 B is the calcspar of another embodiment of Broadboard low-noise low intermodulation distortion receiver of the present invention;

Fig. 5 A is the side circuit of preposition selective filter 15 under differential input among Fig. 4 B;

Fig. 5 B is the side circuit of preposition selective filter 15 under single-ended input among Fig. 4 B;

Fig. 5 C is the connection of circuit application when the multichannel band system of Fig. 5 A or Fig. 5 B;

The preferred embodiment of the low noise amplifier 1 in Fig. 6 presentation graphs 4;

Fig. 7 represents circuit shown in Figure 6 measured input impedance in quite wide frequency domain scope;

Fig. 8 is the preferred embodiment of the buffer 2 among Fig. 4;

Fig. 9 is the preferred embodiment of converter 3 and automatic gain control amplifier 4 among Fig. 4;

After Figure 10 is the processing of 1 to 6 part of radiofrequency signal in Fig. 4, resulting noise coefficient value;

Figure 11 A is the preferred embodiment of the voltage controlled oscillator core 8 among Fig. 4;

Figure 11 B is the preferred embodiment of the resonator 9 among Fig. 4;

Figure 12 represent to utilize Figure 11 A and Figure 11 B the common voltage-controlled oscillator circuit that constitutes carry out free-running structure, wherein Figure 12 A and Figure 12 B represent that respectively the free oscillation that 80MHz is following and 4GHz is above exports;

Figure 13 A and Figure 13 B represent to Figure 11 A and Figure 11 B the common voltage controlled oscillator circuit that constitutes carry out frequency and switch the gained result;

Figure 14 is the preferred embodiment of modulator 11 among Fig. 4, transducer 7 parts;

The schematic diagram that Figure 15 measures for intermodulation distortion;

Figure 16 has low-down intermodulation distortion in order to represent receiver of the present invention;

Figure 17 is used for required actual hardware figure under the situation of cable TV and general radiovision for receiver of the present invention;

Figure 18 is used for actual hardware figure required under the situation of satellite television for receiver of the present invention.

Fig. 4 A represents system block diagrams of the present invention, comprising: differential type low noise low distortion wide-band amplifier 1 (being called for short differential type low noise amplifier or LNA); Direct-current coupling buffer 2 (being called for short buffer or BUF); Voltage/current converter,linear 3 (being called for short transducer or V/I); Differential type low distortion automatic gain control amplifier 4 (being called for short automatic gain control amplifier or AGC); Direct-current coupling buffer 5 (being called for short buffer or BUF); Differential type tracking filter 6 (being called for short IF); Voltage/current converter,linear 7 (being called for short transducer or V/I); Differential type voltage controlled oscillator core 8 (being called for short voltage controlled oscillator or VCOC); Can adjust differential type resonator 9 (being called for short resonator or DCR); Direct-current coupling buffer 10 (being called for short buffer or BUF); The bidirectional balanced formula modulator 11 of low distortion (being called for short modulator or MIX); Direct-current coupling buffer 12 (being called for short buffer or BUF); Intermediate-frequency filter 13 (being called for short IFF); And phase-locked loop controller 14 (being called for short PLLC), wherein the part that dotted line surrounded is represented to do on same integrated circuit.

Fig. 4 B represents the system block diagrams of another embodiment of the present invention, and it is different from Fig. 4 A part and how only has been a preposition selective filter.

The suitable rf frequency scope of this receiver is extremely wide, and from 40MHz to 3GHz or higher, its input signal is the signal that signal that antenna cut down or wired coaxial cable are delivered to, and can be single-ended or the differential wave input.

In the receiver system of Fig. 4 B, the radiofrequency signal of input is introduced into differential preposition selective filter 15 in differential or single-ended (RFin-holds ground connection) mode, this preposition selective filter 15 is a band pass filter, its frequency band and centre frequency are by controlling from phase-locked loop control unit 144 frequency trim signal VTu and channel wave band switching signal BSs, so that selected channel signals passes through, and as far as possible no channel signals is filtered, to reduce the possibility that other channels disturb normal signal, the output signal of this preposition selective filter 15 enters low noise amplifier 1.

On the other hand, in the receiver system of Fig. 4 A, the radiofrequency signal of input directly enters low noise amplifier 1 with differential or single ended mode.

Low noise amplifier 1 amplifies in order to make signal, and it and has the low magnification distortion characteristic of large-signal except having the low noise coefficient, and finishes input impedance matching and output differential wave binomial function.After the output of the differential wave of low noise amplifier 1 prevents from etc. to handle through the Dc bias adjustment of buffer 2, output buffering and adverse current, mode according to balance is connected to transducer 3 with two coupling lines, and then do automatic gain control through automatic gain control amplifier 4 and amplify, wherein the effect of transducer 3 is to cause the large amplitude voltage signal of serious signal magnification distortion to convert relative amplitude less current signal linearly to, converts this current signal to suitable voltage output signal with the distortion level of minimum again through automatic gain control amplifier 4 then.In addition, automatic gain control amplifier 4 utilizes by intermediate frequency output amplitude transducer and taps into amplification or the reduction magnification that the gain control signal GCs that comes adjusts amplifier, make that no matter how the signal amplitude of radio frequency input changes the output amplitude of automatic gain control amplifier 4 all can be kept fixed size.

The output signal of automatic gain control amplifier 4 enters tracking filter 6 after handling through buffer 5, it changes its frequency selective characteristic according to the frequency trim signal VTu from 14 outputs of phase-locked loop controller as Tracing Control signal and channel wave band switching signal BSs, make the radiofrequency signal of the assigned frequency that its tracking desire passes through and the signal of not wanting is filtered its output RFout+ and the one group input (first pass through transducer 7) of RFout-as modulator 11.

Another group input of modulator 11 enters through buffer 10 from 8 outputs of voltage controlled oscillator core, and this group signal also exports the usefulness that phase-locked loop controller 14 is done the channel locking to, and voltage controlled oscillator core 8 required resonant tanks are then provided by resonator 9.The channel data DCs that is provided by outside interface loop imports phase-locked loop controller 14, make it produce corresponding frequency trim signal VTu, be used for adjusting the suitable resonant capacitance value of variable capacitance in the resonator 9, export to lock accurate oscillator signal by the action of the phase-locked loop between loop voltage controlled oscillator core 8, resonator 9, buffer 10 and the phase-locked loop controller 14 simultaneously.

In addition, in order to enlarge the surge frequency range of voltage controlled oscillator, resonator 9 is designed to adjust the differential type resonant tank, and it receives the channel wave band switching signal BSs that enters from phase-locked loop controller 14 and changes different resonant inductance values, uses and switches different channel wave bands.In addition, phase-locked loop controller 14 also utilizes signal VTu as following the trail of the filtering control signal, makes it enter capacitance and the inductance value of switching corresponding wave band that tracking filter 6 changes the variable capacitance in this loop, to finish the function of following the trail of filtering.In addition, the frequency selective characteristic of tracking filter 6 also can reduce the noise coefficient and the intermodulation distortion rate of system.

Transducer 7 constitutes a low intermodulation distortion modulator with modulator 11, wherein transducer 7 receptions are from the output signal (voltage signal) of tracking filter 6, the voltage signal that this amplitude is very big converts relative amplitude less current signal to, and modulator 11 is done bidirectional balanced formula signal hybrid modulation with this group current signal and from the signal of voltage controlled oscillator core 8, process buffer 10.Because the low magnification distortion characteristic in loops such as differential type low noise amplifier 1, buffer 2, transducer 3, automatic gain control amplifier 4 and buffer 5 is added in the prior processing of transducer 7, the intermodulation distortion of modulator 11 can drop to minimum level.After signal after the modulation passes through the buffered of buffer 12 again, export intermediate-frequency filter 13 to, detect required differential intermediate-freuqncy signal IFout+ and IFout-.

Owing to contain all channels from the radiofrequency signal of external world's input, in order to reduce of the interference of non-specified channel signal as far as possible to the specified channel signal, can take the calcspar structure shown in Fig. 4 B, wherein used a preposition selective filter 15 before low noise amplifier 1, its signal of only allowing near the frequency band the specified channel passes through.Fig. 5 A and Fig. 5 B are respectively the preferred embodiment of the side circuit of preposition selective filter 15 under the situation of differential type input and single-ended input, the action of circuit shown in the following key diagram 5A: Fig. 5 A is the preposition selective filter of a switching differential type, its input signal is the radio frequency differential wave of all-channel, switch diode D1, D2 just can enter double resonance formula band pass filter (part of dotted line among Fig. 5 A) when being subjected to wave band switching signal Bx for the high value, wherein comprise two groups of resonant tank: L1, L2, L3 is the inductance of first group of resonant tank, corresponding to different channel wave bands different equivalent inductances is arranged, these inductance also provide the function of impedance transformation, wherein the L2 inductance connects a big resistance R 5 to ground from centre tap, switches diode D1 to provide, the Dc bias path of D2; C, C2 and variable capacitance VD1 are the electric capacity of first group of resonant tank, see through the capacitance that frequency trim signal VTu can change VD1, thereby change equivalent capacitance value.In like manner, the inductance of second group of resonant tank is L1a, L2a and L3a, and electric capacity is C1a, C2a and VD1a.In addition, C3 and VD2 are two groups of coupling capacitances between resonant tank, can change its coupling amount by the capacitance of fine setting VD2.Via above explanation, as can be known by the acting in conjunction of wave band switching signal Bx and frequency trim signal VTu, can change the centre frequency of filter, and adjustable filtering selection function.In like manner, switch the control that diode D3 and D4 are subjected to wave band switching signal Bx, only the signal of filtering gained just can enter the low noise amplifier 1 of next stage when Bx is the high value.Fig. 5 B is the side circuit under the single-ended input condition, and its operating principle is similar to Fig. 5 A, does not add at this and gives unnecessary details.

Fig. 5 C is the connection of circuit application when the multichannel band system of Fig. 5 A or Fig. 5 B, and wherein each square is all represented a filter as Fig. 5 A or Fig. 5 B.The frequency trim signal VTu that each filter is accepted is identical, but wave band switching signal Bx is then independently of one another, because each filter has different equivalent inductances, therefore forms the band pass filter that centre frequency has nothing in common with each other.Can be optionally the mode of a plurality of filters such as Fig. 5 C be connected together, and produces the bandpass filtering effect at the frequency band place of needs (single or multiple).

In addition, very big based on the noise coefficient of preposition selective filter 15 for the noise coefficient influence of whole system, to relax the frequency selectivity of preposition selective filter 15 in design, to guarantee that its loss is below 1dB.

Signal after the preposition selective filter 15 of process is handled is before entering mixer, necessary elder generation is through the pre-process of low noise amplifier 1, buffer 2, transducer 3, automatic gain control amplifier 4, buffer 5 and tracking filter 6, and its major function comprises the amplification of low noise low distortion, automatic gain control and signal selection tracking etc.At first, because the minimum processing of preposition selective filter 15 losses, the noise coefficient of whole system is almost by low noise amplifier 1 decision, in order to pursue minimum noise coefficient, this circuit does not generally have the low noise active member that adopts minimum number, and avoid on RF signal path directly the series resistor element to make input impedance matching, and use the design optimization that inductance or capacitive feedback loop are finished noise and input impedance matching simultaneously instead.Yet this amplifier often causes bigger nonlinear distortion if do not make special linearization process.On the other hand, under this frequency range, optimized inductance or capacitive feedback value are often because can't be integrated within the IC too greatly.In addition, because automatic gain control amplifier 4 receives bigger input signal usually,, must do special linearization process in order to prevent serious magnification distortion.

In order to realize two conflicting characteristics of low noise and low distortion simultaneously, the thinking that the present invention adopts low noise amplifier to separate with the automatic gain control amplifier circuit, please refer to 1 among Fig. 4,2,3,4 and 5 part, wherein as previously mentioned, low noise amplifier 1 is designed to have low-down noise coefficient, and automatic gain control amplifier 4 is designed to have the low distortion characteristic.

Fig. 6 is the preferred embodiment of the low noise amplifier 1 among Fig. 4, active member Q1 and Q2 constitute one group of differential pairing, this differential pairing in conjunction with output electricity group to R1 and R2, need current source Is1 and suitable bias voltage Bias be combined into differential amplifier, in addition, have under the margin (head room) at current/voltage, can be on Q1 and Q2 stacked another group differential pairing Q3 and Q4 increase the enlargement ratio of differentiator.Radiofrequency signal is with the grid of differential mode (grid voltage of transistor Q1, Q2 is respectively RFin+, Rfin-) or single-ended (grid voltage of transistor Q1, Q2 is respectively RFin+, GND) input Q1 and Q2, after amplifying, export in differential mode by the drain electrode of Q3 and Q4 (if do not meet Q3 and Q4, then by the drain electrode of Q1 and Q2).In addition, for the stability and the linearity that increases circuit, use two groups of passive loop Zf1 of negative feedback and Zf2 to be connected to input by output, be connected in series loop or other similar loop and this passive loop can be resistance and electric capacity, they also provide the fixedly input impedance characteristic of wide frequency domain (representative value is 75 Ω) of this differential amplifier institute palpus simultaneously.Fig. 7 represents circuit shown in Figure 6 (about 50MHz-3GHz) measured input impedance in quite wide frequency domain scope, and its size is all between 75 Ω-87 Ω.

The output of low noise amplifier 1 enters before the automatic gain control amplifier 4 earlier the direct-current coupling buffer (being equivalent to the buffer 2 among Fig. 4) through as shown in Figure 8, wherein Q5 cooperates suitable current source Is2 and Is3 respectively as the source electrode following device of forward and negative sense output with Q6, they have the function of anti-stop signal adverse current, and after doing DC decompression by times signal such as grade of its source electrode output through the diode of proper number, provide the input signal of next stage circuit and suitable input stage transistor bias voltage.

Fig. 9 is general commonly used omnidirectional's differential type automatic gain control amplifier circuit, and its big I that gains is decided by top two differential control signal voltage difference delta V, this difference of continuous decrease with obtain-gain more than the 40dB suppresses multiplying power.Please note circuit that Lower Half is made up of transistor Q7 and Q8, resistance R _ f Is3 and Is4 in order to voltage is changed into electric current (being equivalent to the transducer 3 among Fig. 4), as previously mentioned, this circuit improves the linearity of amplifier widely.

With reference to figure 4, after also handling through direct current buffer 5, the output of automatic gain control amplifier 4 picks out the tracking filter 6 of next stage again.The function of tracking filter 6 is identical with preposition selective filter 15, and its side circuit also as shown in Figure 5.But because its loss is very little to the noise coefficient influence of system, so focus on its frequency selectivity in the design, in other words, though tracking filter 6 is finished with all available circuit shown in Figure 5 of preposition selective filter 15, but both have different circuit element main values, and tracking filter 6 is designed to have the narrower frequency band that passes through.The effect of tracking filter 6 is except reducing channel disturbs mutually, and improves the noise coefficient.

Figure 10 is that radiofrequency signal is after foregoing circuit is handled, (about 50MHz-3GHz) resulting noise coefficient value in quite wide frequency domain scope (uses pseudo-morphic High Electfon Mobility Transistor, the PHEMT element), clearly show the noise coefficient very low (less than 4.8dB) of this circuit structure.Because the noise coefficient that other circuit of whole receiver (system shown in Figure 4) increases is very little, so the noise coefficient value of whole system should maintain below the 6dB.

The voltage controlled oscillator core 8 of Fig. 4, resonator 9, buffer 10 and phase-locked loop controller 14 constitute one group of complete phase locked loop system, and the circuit that Figure 11 A and Figure 11 B are combined is a changeable differential type Voltage-Controlled oscillation circuit proposed by the invention.Figure 11 A (being equivalent to 8 among Fig. 4) is the core of Voltage-Controlled oscillation circuit for this reason, belong to multidirectional oscillator structure, comprise one group of differential pairing Q9 and Q10 (also can as stacked another group as Fig. 6 differential to Q17, Q18 to increase enlargement ratio), cooperate one group of output resistance and current source again, constitute a differential amplifier, and two input is inserted through two groups of (Cdg and Cgg) capacitance partial pressures feedback of reporting to the leadship after accomplishing a task by the output of corresponding forward, so produce a multidirectional oscillator loop, when the gain of its loop equals 1 and phase shifts is 360 when spending, just produce stable vibration output.Figure 11 B is the resonant tank of Voltage-Controlled oscillation circuit for this reason, with deciding frequency of oscillation, the signal (with reference to the direction of arrow among figure 11A and Figure 11 B) that is entered by Figure 11 A transistor and drain electrode end separates direct current through two direct currents obstruct capacitor C bk1 earlier, the big resistance R gnd of two ground connection provide resonator must DC path, and variable capacitance VD1 cooperates the direct current iris action of big capacitor C bk2 to constitute the variable capacitance of resonator, the frequency control voltage VTu that phase-locked loop controller 14 produces produces reverse bias through Rc to VD1, makes VD1 present suitable capacitance.On the other hand, the inductance of resonator then is made of with two groups of switching diode pairing Da and Db two groups of La, Lb, the pairing of Lc inductance.Wave band switching signal B1 and B2 (corresponding to the channel wave band switching signal BSs among Fig. 4) by the control diode, can realize the wave band handoff functionality, its action illustrates following (switching to example with the VHF-Low/VHF-high/UHF triband): obtain resonance frequency by vibration theory

f_{osc} = \frac{1}{2 π \sqrt{LC}} - - - - - - (1)

Can make by in suitably selected inductance value La, Lb, Lc:

f_{1} = \frac{1}{2 π \sqrt{LaC}}

Belong to the UHF wave band

f

_{2} = \frac{1}{2 π \sqrt{(La + Lb) C}}

Belong to the VHF-high wave band

f

_{3} = \frac{1}{2 π \sqrt{(La + Lb + Lc) C}}

Belong to the VHF-1ow wave band

(1) when hope produces the UHF audio range frequency, control B1 signal makes two Da diode current flows, and Chnd arrives the path, ground for big electric capacity provides AC signal, therefore has only La and VD1 to constitute resonant tank (Lb and Lc are isolated by ground wire), so can provide the UHF wave band required voltage controlled oscillator function; (2) when hope produces the VHF-high audio range frequency, control B1 makes not conducting of Da control B2 to make the Db conducting then can make (La+Lb) and VD1 constitute VHF-high wave band resonant tank; (3) when hope produces the VHF-1ow audio range frequency, control B1 and B2 make Da and Db all during not conducting, (La+Lb+Lc) constitute VHF-1ow wave band resonant tank (this figure system is an example with the triband resonator, and the resonator of different-waveband number is as long as can finish easily according to Figure 11 B increase inductance and diode group number) with VD1.

Figure 12 represent to utilize Figure 11 A and Figure 11 B the common voltage-controlled oscillator circuit that constitutes carry out free-running result, wherein Figure 12 A and Figure 12 B represent the free oscillation output that 80MHz is following and 4GHz is above respectively, prove that this Voltage-Controlled oscillation circuit can have the oscillating characteristic of utmost point wide frequency domain.

Figure 13 A and Figure 13 B be the function of display frequency switching then, by B1 in the circuit shown in the control chart 11B and B2 signal, finishes frequency and switches between the UHF/VHF-1ow/VHF-high wave band.Figure 13 A is its time domain waveform (top is control signal B1 and B2), and Figure 13 B then is its corresponding frequency spectrum output, and figure can find out that frequency of oscillation becomes 112MHZ (VHF-1ow) by 591MHz (UHF), switches to the result of 257MHz (VHF-high) more thus.

With reference to figure 4, the output of voltage controlled oscillator core 8 is connected to two places after handling through buffer 10, and one is external to the usefulness that phase-locked loop controller 14 is done frequency detecting and locking; Its second input modulator 11 with amplify after the modulation of radiofrequency signal smear.Phase-locked loop controller 14 uses general IC commonly used, the instruction CDs control of its receiving channels data, export one group of wave band control signal (B1, B2 ..., Bn) with frequency trim signal VTu for resonator used.In addition, it compares the voltage controlled oscillator oscillator signal that receives after the internal divider frequency reducing with reference frequency, produces the frequency trim signal output of revising and supplies the usefulness of channel locking.

Figure 14 is a low distortion omnidirectional type smear modulator, can be used as the preferred embodiment of modulator 11 among Fig. 4, transducer 7 parts.Through amplifying the linear current transducer (being equivalent to the transducer 7 among Fig. 4) that enters this circuit below (forming) with the signal (output signal of tracking filter 6 among Fig. 4) of following the trail of filter processor by Q11, Q12, Rf and two current sources, oscillator signal then enter the circuit first half by differentiator that Q13, Q14, Q15 and Q16 formed with modulated radio signal intensity, its output then changes into voltage signal with R2 with current signal by resistance R 1 and gets.This output signal enters next stage intermediate-frequency filter (13 among Fig. 4) again after the processing of buffer circuit (12 among Fig. 4).Intermediate-frequency filter 13 uses the surface acoustic wave element filter usually, can detect the usefulness of final intermediate-frequency (as the 45.75MHz of U.S.'s regulation) for signal demodulation thereafter.

Figure 15 is the schematic diagram that intermodulation distortion is measured, with the signal input receiver processing simultaneously of signal with the non-specified channel fu of specified channel fd, wherein the non-specified channel fu of cable television system be fd every channel, i.e. fu=fd ± 12Mhz; The non-specified channel fu of general broadcast TV then is the adjacent channel of fd, i.e. fu=fd ± 6Mhz.Final medium-frequency IF out should only contain the signal message of fd under the ideal state, but because the cause of receiver intermodulation distortion, have a little fu signal energy and disturb IFout, when the fu energy is more and more strong, this interfering energy is also more and more strong, and when the amplitude that presents on middle frequency domain channel up to this interfering energy reached undisturbed IFout amplitude 1%, the fu energy of input this moment was the index of 1% intermodulation distortion, usually represent with dB μ V that this value represents the intermodulation distortion of receiver littler more greatly.

Figure 16 has low-down intermodulation distortion in order to represent this invention.Dotted line is illustrated in the receiver standard under the 1% intermodulation distortion situation among this figure, solid line then is illustrated in fd=789.25MHz, under the fu=801.25MHz, with regard to various fd signal strength signal intensity, receiver according to the present invention experimentizes, and the intensity of its corresponding AGC control signal also changes (so that IFout strength maintenance certain value) thereupon.Among Figure 16, transverse axis is the fu signal strength signal intensity, is to keep the decay multiplying power that IFout intensity is done and the longitudinal axis is AGC, in other words, is the increase multiplying power of the intensity of fd.Thus figure as can be known the intermodulation distortion rate of receiver of the present invention all to be better than standard under various fd signal strength signal intensity a lot, especially when fd pickup electrode weak (60dB μ V), the fu signal strength signal intensity must just can cause 1% intermodulation distortion rate in intermediate-freuqncy signal greater than 95dB μ V.Generally speaking, under various different fd signal strength signal intensities,, all maintain between the 90-95dB μ V though 1% intermodulation distortion rate is slightly different.It should be noted that in addition this figure is the characteristic of UHF high frequency band, also can keep low intermodulation distortion rate even show receiver of the present invention under high-frequency operation, is that other receivers are incomparable.

More than explanation can represent the good low noise and the distorted characteristic of low intermodulation according to receiver of the present invention in extremely wide frequency domain, and the entire circuit design is suitable for integrated structure fully.The inductive part that is comprised in the dotted line among Fig. 4 all can be integrated into a monocrystalline radio frequency IC, and whole receiver only must be considerably less part just can finish, Figure 17 is for using cable TV of the present invention and the general required actual hardware figure of radio television set system, simple structure extremely is fit to as carry-along micro-receiver.In addition, Figure 18 is for being used in the present invention the method for satellite direct-seeding TV system, because this receiver can be operated more than the 2GHz, from the microwave signal that satellite earth antenna cuts down, the 950MHz after first order differential type low noise amplifier and frequency down circuit processing for the first time can directly enter this receiver system to the radiofrequency signal of 2GHz.Except that this how because native system adopts a frequency converting mechanism, save twice converting system institute must expensive high frequency filter and change-over circuit element for the second time, minimizing number of parts and cost.

Concrete enforcement sample that is proposed in detailed description of the invention or embodiment are only in order to be easy to illustrate technology contents of the present invention, and be not with narrow sense of the present invention be limited to this embodiment, in the situation that does not exceed spirit of the present invention and following claim, can make many variations and implement.

Claims

1, a kind of Broadboard low-noise low intermodulation distortion receiver comprises:

Low noise amplifier receives the differential type of input or single-ended radio frequency signal and with its amplification, has the low magnification distortion characteristic of low noise coefficient and large-signal, and finishes input impedance matching and the function of exporting differential wave;

First buffer receives the output signal of this low noise amplifier, has Dc bias adjustment, output buffering and functions such as adverse current prevents;

First converter receives the output signal of this first buffer, will cause the large amplitude voltage signal of serious signal magnification distortion to convert relative amplitude less current signal linearly to;

Automatic gain control amplifier, receive the current signal that this first converter is exported, convert this current signal to suitable voltage output signal with the minimum distortion degree, and utilize intermediate frequency output amplitude transducer to tap into amplification or reduction magnification that next gain control signal is adjusted amplifier, make the amplitude of its output signal keep fixed size;

Second buffer receives the output signal of this automatic gain control amplifier, is same as this first buffer, also has Dc bias adjustment, output buffering and functions such as adverse current prevents;

Tracking filter receives the output signal of this second buffer, and according to the control signal of input the radiofrequency signal of assigned frequency is passed through, and other signals are filtered;

Second converter receives the radiofrequency signal with assigned frequency that this tracking filter is exported, and converts the large amplitude voltage signal to relative amplitude less current signal linearly;

The voltage controlled oscillator core, resonator, the 3rd buffer and phase-locked loop controller, four constitute a complete phase locked loop system jointly, its annexation receives the control signal of this phase-locked loop controller with the decision frequency of oscillation for this resonator, this voltage controlled oscillator core is connected in this resonator, to have the signal of this frequency of oscillation and shake, this signal that shakes enters this phase-locked loop controller through the 3rd buffer more then, the 3rd buffer has the Dc bias adjustment together, output buffering and functions such as adverse current prevents, this phase-locked loop controller receiving channels data command and to export the wave band control signal used with frequency trim signal this resonator of confession and this tracking filter;

Modulator receive two groups of signals from this second converter and the 3rd buffer, and output signal is the product of these two groups of signals;

The 4th buffer receives the output signal of this modulator, has Dc bias adjustment, output buffering and functions such as adverse current prevents equally;

Intermediate-frequency filter receives the output signal of the 4th buffer, in order to detecting the usefulness of final intermediate-frequency for signal demodulation thereafter,

The noise coefficient of receiver integral body is mainly decided by this low noise amplifier, so the low noise coefficient of this low noise amplifier can guarantee that the noise coefficient of receiver integral body is very low; And then via this first buffer, this first converter and this automatic gain control amplifier three guaranteeing the enlarging function of high linearity, and make the amplitude of output signal of this automatic gain control amplifier keep necessarily; Moreover, owing to the design of respectively partly all taking differential type of receiver, so the stable and attenuating radiation leaking energy of assurance system.

2, as the Broadboard low-noise low intermodulation distortion receiver of claim 1, also comprise preposition selective filter, the poor formula or the single-ended radio frequency signal of input enter before this differential type low noise amplifier, be introduced into this preposition selective filter, in order near the signal the initial option specified channel, and finish the function of impedance transformation as required.

3, as claim 1 or 2 s' Broadboard low-noise low intermodulation distortion receiver, wherein the side circuit of this low noise amplifier comprises:

Become the transistor Q1 and the Q2 of differential pairing, its common source terminal connects a constant current source, and the radiofrequency signal of input is added in the grid place of this Q1 and Q2;

Output resistance R1 and R2, this resistance R 1 is connected between the drain electrode of power supply Vdd and this Q1, and this resistance R 2 is connected between the drain electrode of power supply Vdd and this Q2, and the differential wave of output is the potential difference of the drain potential of the drain potential of this Q2 and this Q1;

Passive loop Zf1 of negative feedback and Zf2, this Zf1 is connected to its grid by the drain electrode of this Q1, and this Zf2 is connected to its grid by the drain electrode of this Q2, in order to fixedly input impedance characteristic of wide frequency domain to be provided.

4, as claim 1 or 2 s' Broadboard low-noise low intermodulation distortion receiver, wherein the side circuit of this low noise amplifier comprises:

Become the transistor Q3 and the Q4 of differential pairing, the source electrode of this Q3 is connected to the drain electrode of this Q1, and the source electrode of this Q4 is connected to the drain electrode of this Q2, and bias voltage is added in the grid place of this Q1 and Q2;

Output resistance R1 and R2, this resistance R 1 is connected between the drain electrode of power supply Vdd and this Q3, and this resistance R 2 is connected between the drain electrode of power supply Vdd and this Q4, and the differential wave of output is the potential difference of the drain potential of the drain potential of this Q4 and this Q3;

Passive loop Zf1 of negative feedback and Zf2, this Zf1 is connected to its grid by the drain electrode of this Q3, and this Zf2 is connected to the grid of Q2 by the drain electrode of this Q4, in order to fixedly input impedance characteristic of wide frequency domain to be provided.

5, as claim 1 or 2 s' Broadboard low-noise low intermodulation distortion receiver, wherein the side circuit of this this voltage controlled oscillator core comprises:

Become the crystal Q9 and the Q10 of differential pairing, its common source is connected to a constant current source, the grid of this Q9 and Q10 is respectively through the two capacitor C gg that equate and ground connection, and the drain electrode of this Q9 connects the grid that capacitor C dg receives this Q10 then, and the drain electrode of this Q10 connects the grid that another capacitor C dg is connected to this Q9 then;

Two resistance R L are connected on respectively between the drain electrode and power supply Vdd of this Q9 and this Q10,

Make to produce a multidirectional oscillator loop, when the loop gain equal 1 and phase shifts be 360 to produce stable vibration output when spending.

6, as claim 1 or 2 s' Broadboard low-noise low intermodulation distortion receiver, wherein the side circuit of this voltage controlled oscillator core comprises:

Become the crystal Q9 and the Q10 of differential pairing, its common source is connected to a constant current source, and the grid of this Q9 and Q10 is respectively through the two capacitor C gg that equate and ground connection;

Become the transistor Q17 and the Q18 of differential pairing, the source electrode of this Q17 is connected to the drain electrode of this Q9, the source electrode of this Q18 is connected to the leakage machine of this Q10, and the drain electrode of this Q17 connects capacitor C dg and receives this grid to Q10 then, and the drain electrode of this Q18 connects the grid that another capacitor C dg is connected to this Q9 then;

Two resistance R L are connected on respectively between the drain electrode and power supply Vdd of this Q17 and this Q18,

7, as claim 5 or 6 s' Broadboard low-noise low intermodulation distortion receiver, wherein this resonator is accepted to determine frequency of oscillation from the wave band control signal of this phase-locked loop controller and frequency trim signal, and its side circuit comprises:

First and second direct current intercepts electric capacity, and first end of two electric capacity is connected to the drain electrode of this Q9 and Q10 in the heart of this voltage controlled oscillator core respectively, in order to direct current is separated;

The big resistance of first and second ground connection, be connected to respectively this first and second intercept second end of electric capacity, the DC path of this resonator institute palpus is provided;

Variable capacitance is connected in second end of this variable capacitance and second end of this second obstruct electric capacity;

Resistance R c, its first end place adds the frequency trim signal from this phase-locked loop controller, its second second end that is terminated at this variable capacitance makes the frequency trim signal produce reverse bias through this resistance R c to this variable capacitance, makes it to present suitable capacitance;

First pair of inductance and first pair of switching diode, first end of this first pair of inductance be connected to respectively this first and second intercept second end of electric capacity, the negative terminal of this first pair of diode is connected to second end of this first pair of inductance respectively, and the anode of this first pair of diode is connected to the first wave band control signal and first ground capacity respectively;

Second pair of inductance and second pair of switching diode, first end of this second pair of inductance is connected to second end of this first pair of inductance respectively, the negative terminal of this second pair of diode is connected to second end of this second pair of inductance respectively, and the anode of this second pair of diode is connected to the second wave band control signal and second ground capacity respectively;

The 3rd pair of inductance, first end of the 3rd pair of inductance is connected to second end of the 3rd pair of inductance respectively, the equal ground connection of second end of the 3rd pair of inductance.

Make and control by this first and second wave band control signal that to produce three kinds of different-waveband signals as follows: when (1) is high when the first wave band control signal, produce high band signal; (2) when the first wave band control signal when being high, produce the medium wave band signal for the low second wave band control signal; (3) be when low when first and second wave band control signal, produce the low band signal, the precise frequency of signal in by each wave band of frequency trim signal controlling.

8, as claim 1 or 2 s' Broadboard low-noise low intermodulation distortion receiver, wherein this tracking filter is formed in parallel by single or multiple band pass filter, and determine which band pass filter to have an effect by channel wave band switching signal, make to produce desirable bandpass filtering effect.

9, Broadboard low-noise low intermodulation distortion receiver as claimed in claim 2, wherein this preposition selective filter is formed in parallel by single or multiple band pass filter, and determine which band pass filter to have an effect by channel wave band switching signal, make to produce desirable bandpass filtering effect.