IL36893A - Receiver rf section - Google Patents

Description

oVpa s? RF p n • This invention relates generally to radio receivers, and more particularly to RF sections of re-r ceivers.

Generally, receiver RF sections or front ends of radios, television and other devices used to receive radiated electromagnetic energy, take various forms in the manner they receive, and, handle RF signal information received at their inputs.. One common arrangement of receiver front end uses the well-known converter stage which operates as a combination oscillator and mixer, and cooperates with the RF signal information received to produce IF signal information of a desired frequency. This type of receiver front end, while having some drawbacks, is widely used because it is relatively inexpensive and requires less power to operate than does the conventional receiver front end which utilizes separate mixer and oscillator stages.

Another type of receiver front end includes RF amplifier stages with one or more stages of amplification to enhance the amplitude of a selected RF signal before it is combined with the local oscillator frequency at the mixer stage. Although receiver front ends which utilize one or more stages of RF amplification together with a separate oscillator circuit to combine frequencies in a separate mixer stage have improved operating characteristics over the converter-type receiver front end, they present a problem in that they are relatively expensive to manufacture and relatively large in size because of the use of coupling transformers between the respective stages ί Λ of the received front end. Also, energizing current is applied to each of the stages of the receiver front end separately and independent of one another since each stage is connected in parallel with the other with respect to receiving energizing current from the power supply of the receiver. This causes a relatively high power consumption within the receiver. Also, the power consumption of the local oscillator within a receiver may be relatively high since there is no means to control the output amplitude of the oscillator frequency signal which is applied to the mixer stage. Therefore, the oscillator circuit also consumes a relatively large amount of power within the receiver. This relatively large consumption of power is of prime concern when operating receivers from a single battery cell where small cells offer limited power availability. These small battery cells will not last very long in prior art systems and then failure may come about at an inopportune moment or without the user being aware of the failure.

The present invention provides a receiver for receiving radio frequency signals information at an input terminal to be converted to intermediate frequency signal information and applied to an intermediate frequency utilization circuit, which includes a power supply circuit to apply operating potential to the receiver for delivering current to a mixer circuit having first and second input terminals and an output terminal which is coupled to the intermediate frequency signal utilization circuit, a local oscillator circuit connnected to the s"ecoftd input of the mixer circuit and arranged to deliver a signal of e e i h is different than the fre uenc mediate frequency signal information, and a radio frequency < amplifier circuit for receiving the radio frequency signals at the input connected in direct current series relation with the mixer circuit through an inductor connected to the sfirsifct input terminal of the mixer, to form a common current path from the power supply circuit through the mixer circuit and radio frequency amplifier.

The present invention also provides a receiver for receiving radiated HP energy comprising RF amplifier means for receiving the RF energy from an input of the receiver and amplifying the RF energy at an output of said RF amplifier means, mixer means having first and second inputs and an output; first means direct current coupling the output of said RF amplifier means in series current relation with the sfirsfi input of said mixer means; oscillator means to generate a signal of predetermined frequency at an output of said oscillator means, said oscillator means having an input terminal; second means direct current coupling the output of said oscillator means to the second input of said mixer means to cause said mixer means to develop an IF frequency signal; an oscillator control circuit having an input and an output; third means direct current coupling the output of said oscillator control circuit to the input of said oscillator means; and fourth means direct current coupling the input of said oscillator control circuit to a circuit point along the direct current connection between said RF amplifier means and said mixer means, whereby the interconnection of the signal path between said RF amplifier means and said mixer means and said local oscillator means and said oscillator control including an inductance element connected in series between th^ < output of said RF amplifier means and said second input of said mixer means and said fourth means being direct current coupled between the input of said oscillator circuit and a tap on said inductance element to control the outputamplitude of said oscillator circuit in response to the amplitude value of said •s predetermined frequency applied to said first input of said mixer means.

The present invention further provides a transistor circuit for amplifying a radio frequency signal and operating from a direct current power supply, including, first and second transistors each having base, emitter and collector electrodes, resonant circuit means including inductor means and capacitor means connected in parallel and resonant at the frequency of the signal, said inductor means including first and second portions having a common junction, and means haying low impedance at the frequency of the signal connecting said junction to a reference potential direct current circuit means connecting said first and second transistors and said impedance matching means to the power supply to provide a series direct current energizing path through said emitter and collector electrodes of said first transistor, said inductor means and said emitter and collector electrodes of said second transistor, first circuit means apply¬ ing a radio frequency signal to said base electrode of said first transistor, and second circuit means connecting said base electrode of said second transistor to a reference potential, said second circuit means having a low impedance at the fre¬ quency of the signal, said resonant circuit means applying portions of said inductor means of said resonant circuit means being selected to match the impedance at said collector electrode of said first transistor to the impedance at said emitter electrode of said second transistor.

One feature of the receiver front end of this Invention la a direct current aeries coupling between the mixer stage and the RF amplifier stage of the receiver such that current flow from the power supply of the receiver Is common between these two stages during operation thereof. This common current flow, or sharing of current, between these two stages of the, receiver front end reduces the total power .consumption of the receiver and enables the receiver to operate for much longer periods of time on battery power supplies, or the like, Another feature of this Invention Is the use of a direct current coupling between the output of the local oscillator of the receiver and one of the Inputs of the mixer stage.

Yet another feature of the invention is the use of a control transistor for controlling the operation of the oscillator of the receiver front end, and where the control transistor has its emitter-base Junction connected in parallel with the emitter-base Junction of the transistor in the mixer stage with respect to DC current.

Briefly, the receiver front end of this inve t tion preferably Includes an RF amplifier stage including a transistor which has its base, electrode direct current coupled to the input circuit of the receiver for, receiving the RF frequency signal , information. The collector electrode of this transistor is direct current coupled to an emitter electrode of a transistor within the mixer stage and this direct current coupling is. preferably through an inductance element. Jn this instance, the inductance element, together with a capacitor connected in parallel therewith, form a tank circuit which matches the impedance at the output of the RF amplifier stage to the impedance at one input of the mixer stage.

A local oscillator stage is provided with a transistor and the collector electrode thereof is direct current coupled to the base electrode of the transistor of the mixer stage to supply the necessary oscillator frequency to combine properly with the RP signal information applied to the emitter electrode of the mixer transistor to develop the desired IP signal information at the output of the mixer stage. The amplitude of the oscillator signal applied to the base electrode of the mixer transistor is controlled by a control transistor which is direct current coupled between the mixer stage and oscillator stage of the receiver front end. Preferably, the control" transistor has the base electrode thereof direct current coupled to the emitter electrode of the mixer transistor, and the emitter electrode of the control transistor is direct current coupled to the base electrode of the mixer transistor, such. that the base-emitter Junctions of the control transistor and mixer transistqr are connected in parallel with respect to a DC current path. Preferably, the transistor within the mixer stage has a DC voltage drop across the base^emitter Junction thereof which is greater than the DC voltage drop across the .base-emitter Junction of the control transistor. This relatively .high voltage drop across the base-emitter Junction of the mixer transistor will cause a relatively high conduction, state of the control transistor which, in turn, causes a high amplitude output of the oscillator transistor to couple a a high amplitude oscillator signal to the base electrode of the mixer transistor . However, the high frequency signal developed across the base-emitter junct ion of the mixer transistor, this high frequency s ignal being only the oscillator frequency signal or the cpmblnation of the RF signal Information from the RF amplifier and the oscillator frequency s ignal of the oscillator stage, will cause reduction in the average DC voltage drop across the base-emitter Junction of the mixer transistor, which voltage drop Is a f unction of the amount of frequency signal injected into the mixer stage . This signal injeo -tion dependent voltage drop across the base-emitter Junc tion of the mixer transistor will cause a reduction of current f lo through the control transistor which, in turn, reduces the signal amplitude of the osc illator frequency signal at the oscillator . This feedback arrangement moBt advantageously controls the amplitude of the oscillator output signal in response to signal information injected Into the mixer transistor .

Most advantageously, bypass capacitors connected to one or mer e of the stages within the receiver front end are coupled back to the power supply of the receiver ■ rather than t o ground potential or some other common reference potential . This enables signal developing resist ors to be connected between each of the transistors in the stage and ground potential, or the common reference potential, and the signal information can be tapped off of these resistors without complicated circuitry .

In one embodiment of this invention the output of the mixer stage is connected to a tank circuit comprls -ing an inductance element and a capacitance element, and the output s ignal developed across this tank circuit is d irec current coupled t o the base electrode of a IP amplifier trans ist or .

In another embodiment of this invent ion the out put of the mixer transist or is connected to a resistor which has a capac it or connected in parallel therewith . In this case als o direct current coupling is used between the resistance-capacitance network and the input of the IP amplifier stage . In the case where the resist or Is used# rather than an induct or, at the output of the mixer stage the resistor serves a d ual funct ion in that it provides means fo developing the IP signal t her ea cross to be applied to the IF amplif ier stage and also serves as a current limiting res istor for the series, connected mixer transistor and RF amplifier transist or .

In the drawings : Figure 1 is a simplified block diagram of a receiver front end constructed in ac cordance with this invent ion; Figure 2 is a detailed schematic wiring diagram of one embodi ment of the receiver front end in accordance with this invent ion; Figure 3 is an equivalent DC circuit arrangement of the receiver front end of Figure 2. illustrat ing the various direct current couplings between each of the tranr sistors within the receiver front end ; and Figure 4 illustrates an alternate embodiment of the receiver front end constructed in accordance with this invention.

Referring now to Figure 1 there is seen a block diagram of a receiver front end which Is designated generally by reference numeral 10. The receiver front end 10 has input means 12, which may be connected to an antenna, for receiving RF signal information radiated from any suitable transmitting station, and which may be of any desired frequency. The RF signal information is converted to an IF signal, in a manner to be described, and applied to an IF signal utilization means 14 which may take any form, and which forms no part qf this invention.

An RF amplifier stage 16 receives and amplifies the RF signal information from the input means 12 and applies it to an input 18a of a mixer stage 18. Operating potential from a B+ eupply is applied to an input terminal 20 of the mixer stage 18 and common current flow will pass through the mixer stage 18 and through the RF amplifier stage 16 as a result of a direct current coupling 22 which connects the output of the RF amplifier stage 6 to the input 18a of the mixer stage 18. Thie direct current series coupling between the mixer stage and the RF ampll-fier stage substantially reduces the current requirement for operating these stages as compared to the current requirement if they were operated by independent current paths as is usually the case. That is, current flow from the B+ source which passes through the mixer stage 18 is also common with the current flow passing through the RF amplifier stage 16 thus resulting in a substantial saying in a power dissipation In operating these two stages.

A local oscillator circuit 24 has its output terminal 24a direct current coupled to a second input 18b of the mixer stage 18 so that the RF signal and the oscil- lator signal will be heterodyned within the mixer stage to produce a difference frequency which is the desired IF frequency. B providing direct current coupling between the output terminal 24a of the oscillator 24 and the second input terminal 18b of the mixer stage 18, a savings in AC coupling components is realized, i.e. the use of transformer coupling is eliminated. This direct current c§ypl= ing toget er with the direct current coupling between t e mixer 18 and the RP amplifier 16 enables t e receive?' front end 10 to be made relatively small in size with a minimum of components and at a substantially reduced cost, as compared to receiver front ends known heretofore.

To insure that the signal level applied to the input terminal 18b of the mixer 18 is of the proper value, an oscillator control circuit 26 has an output terminal 26a thereof direct current coupled to an input terminal 24b of the oscillator 24 to control the amplitude of oscillations of the oscillator. This control of amplitude of the oscillator, frequency signal is obtained by a paral-lei connection of the input terminals 26b and 26c with that of the input terminals 18a and 18b, respectively, of the mixer stage 18. The oscillator control circuit 26 is then controlled in response to the potential across terminals 18a and 18b which, in turn, is of a value proportional . to the amount of signal injected into the mixer stage 18. For example, when the signal level from the output of the oscillator 24 is much higher than the signal level from the RF amplifier 16, the potential across terminals 18a and 18b will decrease to correspondingly decrease the out-put signal from the oscillator control circuit 26 which, in turn, decreases the amplitude of the signal of the oscillator circuit 24. This novel circuit arrangement provides a closed loop feedback responsive to signal injection at the mixer stage 18 so as to always provide the proper signal levels between the RF frequency signal at terminal 18a and the oscillator frequency signal at terminal 18b to obtain proper mixing of the signals to develop, the desired IF signal frequency Information, An IP amplifier stage 28 as its input erminal 28a direct current coupled to output terminal l§c of the mixer stage 18 to amplify the IF signal and apply it to the IF signal utilization means 14. However, ί-t will be understood that the IF amplifier stage 28 may be incorporated within the IF signal utilization means 14, if desired.

Referring now to Figure 2, there is seen a detailed schematic diagram of the receiver front end 10 ilr lustrating one preferred arrangement of direct current coupling between the various stages of the receiver front end. Here it can be seen that the RF amplifier stage 16 includes a transistor 30, illustrated as an NPN type, with Its base electrode direct current coupled to the input terminal 12 via a line 31 and a portion of an inductance element 32. A capacitor 33 is connected in parallel with the inductance element 32 to form a tank circuit which is t,uned to a frequenpy corresponding to the desired incoming RF frequency signal information. The capacitor 33 is here illustrated as being of a fixed capacitance value, but it will be understood that a variable capacitor may be used so as to provide a tuned input circuit which can be varied In frequency within a given frequency range . In the alternative/ the Inductance element 32 may be variable to provide the necessary variable tuning of the tank circuit .

A resistor 3^ Is connected between the emitter electrode of transistor 30 and a line 35, the line 35 being the common reference potential s uch as ground potential .

The mixer stage 18 comprises a transistor 36, here being illustrated as NPN type, havin its emitter electrode direct curypnt coupled to the c ollect or elec - 10 trode of transistor 30 via the line 22. Preferably, an inductance element 37 is interposed In the line 22 and has connected in parallel therewith a capacitor 38 to form a tank circuit which, at the frequency developed , within the RP amplifier stage 16, matches the output impedance of the he inductance. eleme¾a§?M0r M pWctt d by1 capacitor 67 connected by conductors ,68, and 56. tq B+ . , , . . , _ . transistor 3o at the emitter electrode thereof , / Therefore, impedance matching to the input of the base of transistor 30, is accomplished by the tank circuit formed by the Inductance element 32 and capacitor 33, and imped - 20 ance matching at the output of transistor 30 is accomplished by the inductance element 37 and 38. By utilizing the tank circuit formed by inductance element 37 and capacit or 38 within the direct current path between transistors 30 ; and 36, phase reversal or neutralizing of the signal developed by the RF amplifier stage l6 is readily accomplished by a single capacitor 39 which has one end thereof con^ '•v nected to the base electrode of transistor 30 and the other end connected to the collector electrode of transistor 30 via the inductance element 37. Capacitor 39 also serves as a bypass capacitor for IF frequency signal, inf ormation which may be developed at the emitter electrode of transist or 36. Preferably, the base electrode of transistor 30 is connected to a bypass capacit or 4p t hro ugh the inductance element 32, and the other end of this bypass capacit or is connected to the B+ line of the receiver rather tha t o ground potential or the reference potent ial at line 35.

The oscillator circuit 24 includes a transist or 41, illustrated as an PN type, with the collector eleo -trode thereof direct current coupled t o the base electrode of the transistor 36 of the mJx er stage 18, The direct current coupling between the oscillator circuit 24 and the mixer stage 18 eliminates t he need of AC coupling device such as capacit ors or transformers or the like . The osc-cillator signal at the bas e electrode of transistor 36 together with the RF frequency signal inf ormat ion at the emitter electrode of transistor 36 are combined to develop a difference frequency signal of the desired IP frequency . This IP frequency s ignal informat ion is then developed within a tank circuit comprising an inductance element < 42 and a capacitor - 43 which are connected to the collector electrode of transistor 36. The IP frequency signal inr-f ormatlon developed at the output of mixer stage is then direct current coupled to the IP amplifier stage 28 via a line 44 .

The transistor 41 of the oscillator circuit 24 has the emitter electrodes the reof connected to the line 35 through a resistor 4 . The emitter electrode of transistor 41 is also connected to a tank circuit comprising an inductance element 46 and a piezoelectric element 47 thereby forming a crystal controlled oscillator with the transistor 41 , Connected to the inductance element 46 and the piezoelectric element 7 are a pair of capacitors 48 and 9 which are tied together at a circuit point 50, and an inductance element 51 is connected in parallel with the capacitors 48 and 49. Although, the translator 41 together with the piezoelectric element 4 f orm a crystal controlled oscilla r of a fixed frequency, it may be desirable to provide a va iable frequency o§eiUat© which tracks a variable frequency input tuned cir uit c nnec ed at the input terminal 12 go that the receiver front end . 10 may receive the given band of frequencies , Most advantageously, the oscillator control circuit 26 includes a transistor 52, illustrated as a PNP type, with the collector electrode thereof connected to the line 3 via a resistor 53. The base-emitter Junction of transistor 52 is connected in parallel with the base-emitter Junction of transistor 36 of the mix er stage 18, and, as such, the transistor 52 will conduct in response to the voltage drop across the two inputs of the mixer stage, i. e . the base ard emitter of transistor 36, correspondingly to control the amplitude of the output signal of the oscillator circuit 24. That is, the base electrode of transistor 52 is connected to a center tap 37a on the Inductance element 37 via a line 54 and therefrom to the emitter electrode of transistor 36. On the other hand, the emitter electrode of transistor 52 is connected to the base electrode of transistor 36 via line 56, a line segment 57, and the inductance element 51, where the line segment 57 forms part of a B+ distribution line to the various components of the receiver front end 10, Since the transistor 52 of the oscillator control circuit 26 is used as a DC operated control device to control the output level of the oscillator circuit 2 , the connection to the base electrode of transistor 36 via a portion of the B+ distribution line, i.e., the line segment 57, is readily utilized as a current path for its operation, Preferably, transistor 36" Qf th© mJL¾er stage 18 is selected to be a high frequency tranjistpr. Which is a. classification of transistors, welle-known in the art, while the transistor 52 of the oscillator control circuit 26 is selected to be a low frequency transistor. Therefore, the characteristic diode voltage developed across the base-emitter junction of transistor 36 will be greater than the characteristic diode voltage developed across the base-emitter Junction of transistor 52 when given DC bias currents are maintained through the base-to-emitter Junction of these transistors. In the illustrated embodiment, the characteristic diode voltage of transistor 36 may be. in the order of 50 to 100 millivolts, more or less, greater than the characteristic diode voltage across the base-emitter Junction of transistor 52, this voltage range beting given only by way of example. However, upon application of a high frequency signal to the base electrode of transistor 36, from the output of the oscillator 24, the base-emitter voltage of transistor 36 can decrease to a level lower than the characteristic diode voltage drop across the base-emitter junction of transistor 52. This decrease in base-emitter voltage at the mixer transistor 36 correspondingly decreases the output of transistor 52 which, in turn, decreases the amplit ude of the osc illat or frequency signal from transistor 41 , Hence, a closed loop feedback circuit is provided between the input' and output terminals of the osc illator circuit 24 and is responsive t o the level signal inject ion at the mixer stage 18.

The IP amplifier stage 28 includes a transist or 60 which has the base electrode thereof connected t o the line 44 t o receive the JF frequency signal information developed at the output of mixer stage 18, A signal de-veloplng resist or 61 is connected between the collect or electrode of transist or 6b and the B+ line, and the emitter electrode of trans iptor 60 is also c onnected to the Byline through a bypass capacitor 62 , A resistor 63 is connected between the emitter electrode of transistor 60 and the line 35 to provide an operating current path for the trans istor 60.

Most advantageously, all of the bypass capacit ors that are used in the receiver front end 10 are connected back to the B+ line rather than being connected t o ground potent ial or a reference potential at the line 35. For example, the base electrode of trans istor 41 of the oscillator stage 24 has a bypass capacit or 65 connected t o the B+ line via the line 66 and the line 56. Similarly, the base electrode of transistor 52 of the oscillator control circuit 26 has a bypass capacit or 67 connect ed t o the Byline through a line 68 and the line 56. The emitter elec trode of transist or 30 of the RP amplifier stage 16 has a bypass capac itor 69 connected to the B+ line through the line 56. The tank c ircuit f ormed by the inductance ele-ment 42 and capacitor 43, together with the tank c ircuit formed by the capacitors 48 and 4 ο, and the Inductance element 51, provide operating potential to transist ors 36 and 41,, respectively and, as such, the transistors 36 and 41 have their RF ground at the B+ connection. Therefore, by connecting ail other bypass capacitors in the circuit to the B+ line, It enables each of the resistors 34 , 53 , 45 and 63 to become signal developing resistors so that direct current coupling, as for example between the collector electrode of transistor 52 and base electrode of transistor 41, is readily obtained without the use of AC coupling components , Referring now to Figure 3, there is seen a s implified schematic diagram of the circuit arrangement of Figure 2 with only the direct current connections illustrated to facilitate a clearer understanding of the novel concepts of this invention. The component s in Figure 3 are designated by the same reference numerals at the corresponding components in Figure 2 to facilitate a ready referen ce back to Figure 2 to understand the operation of the circuit . A bias reference potential which may be from an external source, is applied to the base electrode of transistor 30 and ^Lts voltage value Is selected to cause transistor 30 to conduct and develop a voltage of approximately 0.1 volt , more or less, , across the resistor 34 in the emitter circuit of transistor 30, This arrangement will caus the transistor 30 to. act as a current source for the RF amplifier stage 16 and the mixer stage 18. The base-emitter Junction of transistor 36 is here illustrated within a dotted line and is designated by reference numer*-al 36a . The base-pemltter Junction 36a is connected in parallel with the base-emitter junction of transistor 52, this parallel connection being a direct current connection. As mentioned hereinabove, transistor 36 is selected to be a high frequency transistor while transistor 2 is selected to be a low frequency transistor .

Since the base-emitter voltage drop across voltage transistor 36 Is in the order of 0τΊ00 millivolts, more or less, greater than the base-emitter voltage drop across transistor . the transistor 52 will be rendered highly conductive . Tp achieve a higher voltage drop with-* in the base-remitter circuit of transistor 36 it will be understood that a diode or resistor may be connected in series In the line 36b at the base electrode of transis tor 36. in this case the transistors 36 and 52 may be of the same type, as desired .

Conduction of transistor 30 in respons e to the value of the bias reference voltage at the base thereof, will cause current flow to pass between the emitter-base Junction of transistor 52 causing It to conduct . The state of conduction of transistor 52 may be relat ively high because of the voltage drop across the base-emitter junction of transistor 36, and possibly may be conductive to a stage of saturation. As a result of the direct current coupling between the collector electrode of transistor 52 and the base electrode of transistor 41 the transistor 41 will conduct to a value corresponding to the conduction of transistor 52, that is , high conduc tion state of tran^ sistor 52 will cause a corresponding high conduction state of translator 41. However, transistor 41 forms the oscil-lator transistor of the oscillator circuit 24 and high con- auction of transistor 41 will produce high amplitude output of the oscillator frequency signal applied to the base electrode of the mixer transistor 36. Referring ba k to the base-emitter Junction 36a of transistor 36, the high frequency output of the oscillator circuit 2 which Is applied to this Junction causes the characteristic diode voltage developed thereacross to decrease with Increas ing amplitude of the oscillato frequency signal. Therefore, with an osc illator ency signal present at? the base-emitter Junct ion of translator 36 the voltage drop across this Junction Is decreased , and can be decreased to a level lower than the voltage drop across the base-emitter Junction of transistor 52. This action ll tend to render transistor 52 nonconductive or substantially nonconductlve resulting in a substantial reduct ion of current flow through the oscillator transistpr 41 which, in turn, decreases the oscillator signal output t o the base electrode of transistor 36. Therefore, there is provided a direct current coupling feedback loop between the oscil-lator transistor 41 and the mixer transistor 36 with the control transistor 52 connected in a manner to control current in the feedback loop. This feedback loop causes the high frequency output of the oscillator to be controlled continuously to a value to be Just large enough to cause a characteristic diode voltage drop at the base-emitter Junction of transistors 36 and 2 to be substantially equal . This being the condition which provides optimum operation of the oscillator circuit 24 with minimum current through the transistor 41.

Ey controlling the oscillator circuit 24 in re- spons e to the amount of osc illator signal injected into the mixer c ircuit stage 18, the osci llat or will draw; only the necessary amount of current from the B+ supply t o develop an oscillator frequency signal of the desired amplit ude to provide proper mixing thereof w ithin the mixer stage 18, and thus enhance the power saving capabilities of the receiver front end 10. This feat ure, t ogether with the feature of common current flow between the RF amplifier trans istor 30 and mince transistor 36, enables the receiver front end c ircuit 10 t o be operated' w ith a B+ voltage supply of about 1 t o 1- volts with a minimum of current draw from the power supply . The power supply may be a dry cell battery, or the like, and the receiver to operate for a longer period of t ime with a given type of battery than would a receiver of convent ional design.

The bias reference voltage applied t o the base electrode of transistor 30 may be obtained from a separate reference voltage source which will set the level of oper-ation of the receiver front end 10, or the bias reference voltage may e obtained by a voltage feedback from the IF amplifier stage 28 as illustrated in Figure 4 .

Referring to Figure 4 there is seen an al ternate embodiment of a receiver front end constructed in accord ance with this invention and is here designated generally by reference numeral 70. Here also, an RF amplifier stage 71 has a transistor 72 with its load electrodes direct current coupled to the load electrodes of a trans istor 73 within a mixer stage 74. This direct current , coupling ber-tween the transietors 2 and Is referabl obtained via an inductance element 76 which has a tap 76a direct current coupled to the base electrode of a translator 76 w hich forms an os cillat or control circuit 78.

Connected in parallel with the inductance element 76 is a capac it or 79 which forms a tank circuit with the inductance element to mat ch the output Impedance of the transistor 72 to that of the input impedance of the trans istor 73 at the emitter electrode thereof . The base electrode of transistor 72 is direct current coupled to an input terminal 12a v a a portion of an Inductance element 80 which, together with a capacitor 81 forms a tank circuit tuned to the desired incoming RP frequency . In this Instance also capacitor 81 ma be a variable capacitor, or for that matter inductance element 80 may be a variable inductance, to provide tuning of a tank c ircuit over a given band of frequencies to be received by the receiver front end 70. A bypass capacitor 82 is connected • between the tank circuit formed by inductance element 80 and capacitor 81 and the B+ terminal .

In t hiB instance, the output of the mixer stage 7 is connected t o a resist or 83 and a capacitor 84 , This Is in contrast t o the tuned circuit at the out put of the transistor 36 of Figure 2. In this embodiment the resistor 83 serves a d ouble function in the pircult as it provides a load for the mixer transistor 73, across which is developed the IF signal information, and also provides means for meas uring and eventual control of the c urrent f low through the mixer transistor 73 and RF amplifier trans istor 72. Also, current through the series transistors 72 and 73 can be measured by measuring the voltage drop across resistor 83 which is of a known resistance value.

An oscillator circuit 86 includes a translator 87 the base electrode of which is direct current coupled to the collector electrode of transistor 77 In the oscillator control circuit 78. The bias voltage for transistor 87 is developed across a resistor 88 connected in series with transistor 77 to a common line 89 which may be a common reference potential or ground poten ial, The collector electrode o transistor 87 3-3 con ec ed to the B+ line through an inductance element: 90, and the baae emitter Junction of transistor 77 Is connected in parallel with the base^emltter Junction of transistor 73 via a line 91 and the inductance element 90. Connected In parallel with inductance element 90 are a pair of capacitors 92 and 93 which are connected together at a circuit point 9 which, in turn, is connected to a tuned circuit comprising an inductance element 96 and a piezoelectric element 97 which form a fixed frequency oscillator with the transistor 87. The oscillator circuit 86 may be a variable fre-quency oscillator circuit when the tuned circuit comprise ing lnductanpe element 80 and capacitor 81 is also a variable frequency circuit so that the receiver front end 70 may tyack a given band of frequencies. Connected in series with the transistor 87 is a resistor 98 and the output of the oscillator circuit 70, i.e., the collector electrode of transistor 87, is direct current coupled to the base electrode of transistor 73 via a line 99. This circuit arrangement provides the closed loop feedback for controlling the output of the oscillator circuit 86 as de-scribed hereinabove with regard to the receiver front end • ) * of Figure 2 , The IF frequency signal Information deveioped across resistor 83/ at the output of mixer stage 7 , is direct current coupled to the base electrode of a transistor 100 which forms a first IF amplifier, stage within the receiver front end 70, This direct current coupling is over a line 101 ^nd through a diode 102. Also connected tP the Junction of the base electrode of the ran^ sistor loo an the cat hode elec rode of the diode 102 is a resistor 103 , The trans istor 100 provides a irst stage of IF amplification by developing the IF signal across a resistor 104 and applying this signal to the base electrode of a second IF amplifier translator 106. The emitter electrode of the first IF amplifier transistor 100 is connected to the B+ supply through a res istor 107 which is parallel by a bypass capacitor 108. The second IF amplifier transistor 106 has conneqted in series therewith a first resistor 109 which is also connected in series with a second resistor 110, which, in turn, is parallel by a bypass capacitor 111. The resistors 109 and 110 provide a voltage divider network so that a voltage value de^ veloped at a circuit point 112 between the resistors can be direct current coupled back to the base electrode of transistor 72 at the RF amplifier stage 1 via a line 113 and through the inductance element 80. This direct current coupling feedback between the last IF amplif ier stage and the RF amplifier stage 71 provides means, for controlling the overall current through the RF amplif ier and mixer stages 71 and 74, respectively, while also providing an enhanced IF signal information signal to, be applied tp the IP utilization means , as illustrated In Figure 1 , The receiver front end 70 in Figure operates substantially in the same manner as the receiver front end 10 of Figure 2. That is, common current flow between the RF amplifier stage 71 and the mixer stage occurs between the collector emitter electrodes of the transistors in these stages and through an Inductance element connected In series therewith. A tap on the Inductance element 76 is direct current coupled to the baae electrode of the oscillator control transistor 77 which, in turn, has Its collector electrode direct current coupled to the base electrode to the oscillator transistor 87. The base-emitter Junction of transistors 73 and 77 are connected in parallel one with the other with respect to a DC current path, and the output signal from the oscillator transistor 87 is direct current coupled to the base electrode of the mixer ' transistor 73.

The direct current circuit couplings between the various components of the receiver front end 70 is sub-stantially the same as that shown in Figure 3 with regard to the receiver front end 10. The only difference being that an additional stage of IF amplification is provided and a direct current coupling feedback Is provided between the second IF stage and the input of the RF amplifier stage . Also, in this embodiment, a diode ie connected in series with the direct current coupling between the output of the mixer stage and the input of the IF amplifier tranr. sis tor 100.

Accordingly, the receiver front ends 10 and 70, of the illustrated embodiments, provide a unique and novel circuit arrangement in which the interconnection between the various active circuit components of all of the stages are direct current coupled, thereby eliminating the need of AC coupling devices such as capacitors or transformers. Also, a substantial power saving is obtained by having a common current flow passing through the mixer stage and the RP amplifier stage and wherein oscillator current is minimized as a result of a direct current feedback loop created between the output of the oscillator and the input of the oscillator, which feedback signal is controlled in response to the amplitude of the signal injection at the input of the mixer stage. Accordingly, it will be understood that variations and modifications of this invention may be effected without departing from the spirit and scope of the novel concepts disclosed and claimed herein.

Claims (16)

36893/2

1. A receiver for receiving radio frequency signals information at an input terminal to be converted to intermediate frequency signal information and applied to an intermediate frequency utilization circuit, which in¬ cludes a power supply circuit to apply operating potential to the receiver for delivering current to a mixer circuit having first and second input terminals and an output terminal which is coupled to the intermediate frequency signal utilization circuit, a local oscillator circuit con- segond nected to the fire-t input of the mixer circuit and arranged to deliver a signal of predetermined frequency which is different than the frequency of the radio frequency signal information to develop the intermediate frequency signal information, and a radio frequency amplifier circuit for receiving the radio frequency signals at the input connected in direct current series relation with the mixer circuit through an inductor connected to the ¾£i>!ftd input terminal of the mixer, to form a common current path from the power supply circuit through the mixer circuit and radio frequency amplifier.

2. The receiver of claim 1, wherein the local oscillator circuit has a control circuit with the output thereof direct current coupled to the first input of the mixer .

3. The receiver of claim 1 or 2, wherein the mixer includes a current control device having load electrodes, and the radio frequency amplifier circuit includes a current control device having load electrodes, with the 36893/2 current series with one another.

4. The receiver of claim 1, 2.or.3, wherein the oscillator circuit includes a control circuit which is. connected to a tap of the inductance element to control the output amplitude of the oscillator in response to the amplitude value of the oscillator frequency which is applied to the first input of the mixer.

5. The receiver according to any one of the preceding claims, wherein the mi..er includes a transistor, the oscillator circuit being controlled by a control circuit having a transistor and the base-emitter junctions of the transistors being connected in parallel with one another.

6. The receiver of claim 5, wherein the mixer transistor is a high frequency transistor and the oscillator control transistor is a low frequency transistor, the low frequency transistor developing a voltage drop between the base-emitter junction thereof, when forward biased by a BC voltage, which is less than the voltage drop across the base-emitter junction of the transistor.

7. The receiver according to any one of the preceding claims including an inductance element and a capacitance element forming a tank circuit at the input of the RF amplifier, an input terminal being coupled to a tap on the inductance element, the IF amplifier stage having an input direct current coupled to the output of the mixer, and an output signal from the IF amplifier being direct current coupled to the input of the RF 38893/2 a reference voltage to the RF amplifier in accordance with the amplitude of the output signal of the IF amplifier.

8. The receiver of claim 7, including a diode connected in the line between the output of the mixer and the input of the IF amplifier stage.

9. The receiver of claim 1 wherein the inductor has a tap thereon connected to a bypass capacitor, and further including a capacitor connected in shunt with the inductor and forming a tank circuit therewith for matching the output impedance of the radio frequency amplifier circuit with the input impedance of the mixer circuit.

10. The receiver of claim 1 or 9, wherein the radio frequency amplifier circuit includes a transistor having a base electrode to which the radio frequency signals are applied and a collector electrode connected to the inductor, and further including a neutralizing capacitor connecting the end of the inductor remote from the collector electrode of the transistor to the base electrode thereof.

11. A receiver for receiving radiated RF energy, comprising RF amplifier means for receiving the RF energy from an input of the receiver and amplifying the RF energy at an output of said RF amplifier means; mixer means having first and second inputs and an output; first means direct current coupling the output of said RF amplifier means in series current relation with the 80808/3 generate a signal of predetermined frequency at an output of said oscillator means, said oscillator means having an input terminal; second means direct current coupling the output of said oscillator means to the second . ■£i &€ input of said mixer means to cause said mixer means to develop an IF frequency signal; an oscillator control circuit having an input and an output; third means direct current coupling the output of said oscillator control circuit to the input of said oscillator means ; and fourth means direct current coupling the input of said oscillator control circuit to a circuit point along the direct current connection between said RF amplifier means and said mixer means, whereby the interconnection of the signal path between said RF amplifier means and said mixer means and said local oscillator means and said oscillator control circuit are formed by direct current couplings, said first means including an inductance element connected in series between the output of said RF amplifier means and said second input of said mixer means and said fourth means being direct current coupled between the input of said oscillator circuit and a tap on said inductance element to control the output amplitude of said oscillator circuit in response to the amplitude value of said predetermined frequency applied to said first input of said mixer means.

12. The receiver of claim 9, wherein said direct current coupling means between the tap on oscillator circuit includes the juncture of a load \K" electrode and a control electrode of said oscillator control circuit, and a bypass capacitor having one end thereof connected to the control electrode of said current control device and the other end thereof arranged for connection to a power source of the receiver.

13. A transistor circuit for amplifying a radio frequenc signal and operating from a direct current power supply, including, first and second transistors each having base, emitter and collector electrodes, resonant circuit means including inductor means and capacitor means connected in parallel and resonant at the frequency of the signal, said inductor means including first and second portions having a common junction, and means having low impedance at the frequenc of the signal connecting said junction to a reference potential, direct current circuit means connecting said first and second transistors and said impedance matching means to the power supply to provide a series direct current energizing path through said emitter and collector electrodes of said first transistor, said inductor means and said emitter and collector electrodes of said second transistor, first circuit means applying a radio frequency signal to said base electrode of said first transistor, and second circuit means connecting said base electrode of said second transistor to a reference potential, the frequency of the signal, said resonant circuit -means applying the signal from said collector electrode of said first transistor to said emitter electrode of said second transistor, said portions of said inductor means of said resonant circuit means being selected to match the impedance at said collector electrode of said first transistor to the impedance at said emitter electrode of said' second transistor.

14. A transistor circuit in accordance with claim 13, including circuit means connected to said second transistor forming a mixer circuit therewith, and including means applying a local oscillator signal to said base electrode of said second transistor and means deriving an intermediate frequenc signal from said collector electrode. of said second transistors.

15. A transistor circuit in accordance with claim 13, further including local oscillator means for providing a local oscillator signal, control means for said local oscillator means coupled to said inductor means for controlling the amplitude of the local oscillator signal in accordance with the signal in said inductor means, circuit means connecting said local oscillator means to one of said first and second transistors for applying said local oscillator signal thereto, whereby said local oscillator signal is mixed with the radio frequenc signal to produce an intermediate frequency signal.

16. A receiver for receiving RF signal information S, HOROWITZ & CO. AGENTS FOR APPLICANTS