Frequency-conversion mixer

Abstract: A frequency-conversion mixer which is designed to operates in substantially the whole range of a radio frequency band extending from the low-frequency to the ultra-high-frequency. The frequency-conversion mixer comprises input means including a first and second diode arranged in inverse-parallel connection with each other, detecting means including a third and fourth diode arranged in series connection with each other, and a dc component removing capacitor connected to an output side of the input means and a junction point between the third and fourth diodes whereby the use of transformers such as used in a double balanced mixer is eliminated and there is practically no output response at frequencies below the cutoff frequency of the diodes.

Description: The present invention relates to a frequency-conversion mixer which operates within substantially the whole range of the radio frequency band extending from long wave or low-frequency to ultra-high-frequency and higher. US-A-3 983 489 describes a balanced doubling mixer incorporating first and second diode means. Each diode means includes at least two semiconductor diodes connected in parallel and oriented oppositely. 1988 IEEE MTT International Microwave Symposium Vol. II, 25 - 27 May 1988, New York, US, pages 695 - 697, J.L. Merenda et al. "4 to 40 GHZ even harmonic Schottky mixer" discloses a doubly balanced diode mixer incorporating four diode means. Each diode means includes two diodes connected in parallel and oriented oppositely. Referring now to Fig. 7, there is shown a type of diode mixer which has been used in ordinary transmitters, radars, etc., involving frequencies higher than the ultra high frequency band. A signal R of a frequency f₁, which has been received through a tuning circuit 1, is coupled with a local-oscillator signal OSC of a frequency f₂,mixed by a diode 2 and outputted as an intermediate frequency signal IF of a frequency f₁ + f₂ or |f₁ - f₂| through a tuning circuit 3. Such diode mixers have large conversion loss and, frequently, coupling loss due to the inevitable use of magnetic coupling for the tuning circuit and thus restrictions are imposed on obtaining the best coupling. Also, Fig. 8 shows a circuit diagram of the double balanced mixer. The double balanced mixer includes 4 diodes D₁, D₂, D₃ and D₄ which are connected in a ring form so that when, a receiving signal R is applied via an input-output transformer T₁ and also a local-oscillator signal OSC is applied between the secondary side of the input-output transformer T₁ and the primary side of an input-output transformer T₂, an intermediate frequency signal IF of a frequency f₁ + f₂ or |f₁ - f₂| is generated through the input-output transformer T₂. The double balanced mixer has been designed so that the local-oscillator signal OSC does not leak from the mixer circuit. As a result, the cross modulation distortion characteristic is excellent as compared with that of vacuum mixers, transistor mixers and diode mixers. In addition, the oupled circuit can be coupled directly and is therefore, at present, the best mixer. As a result, if the circuit design of the double balanced mixer is correct, the mixer circuit itself operates positively and no adjustment is required. Thus, the double balanced mixer is used in a variety of circuits. However, double balanced mixers have the disadvantage that their electric characteristics are largely dependent on the characteristics of their component parts such as the diodes and transformers thus requiring careful selection of component parts depending on the frequency band used. Also, it has been required that the output of the local-oscillator signal is between 10 and 30 dbm. There has existed another disadvantage, i.e. that there are instances where the output of the local-oscillator signal corresponds to the transmitted output in microwave, resulting in a high cost just for the circuit generating the local-oscillator signal. Further, the double balanced mixers have the disadvantage that they are high in conversion loss compared with mixers of the other types thus requiring the provision of an amplifier on the output side. The present invention has been made with a view to overcoming the stated deficiencies in the prior art, and it is an object of the present invention to provide a frequency-conversion mixer which can be used in either concentrated constant circuits or distributed constant circuits and which is capable of reversible conversion. To accomplish the above object, in accordance with the present invention there is provided a frequency conversion mixer as claimed in claim 1. When the signal of the first frequency is applied to the input means and the signal of the second frequency is applied to the detecting means, a signal of a frequency representing the sum or the difference between the first and second frequencies is generated through the dc component removing capacitor. Thus, there is the effect of providing a frequency-conversion mixer which eliminates the use of such transformers as used in double balanced mixers and which practically has no output response at frequencies below the cutoff frequency of the diodes. Also, there is the effect of providing a frequency-conversion mixer in which each pair of reverse connected diodes functions as a coupling capacitor of the proper capacitance thus practically eliminating the attenuation of signals and ensuring the reduced passing loss of signals. The above and other objects as well as advantageous features of the invention will become more clear from the following description taken in conjunction with the drawings, which show in Fig. 1 a circuit diagram of a frequency-conversion mixer according to an embodiment of the present invention; Fig. 2 a schematic diagram useful for explaining the input-output relation of the frequency-conversion mixer shown in Fig. 1; Fig. 3 a circuit diagram of a frequency conversion mixer according to another embodiment of the present invention. Fig. 4 a perspective view of a frequency-conversion mixer of a modular construction; Fig. 5 a circuit diagram of a receiver in which is mounted the frequency-conversion mixer shown in Fig. 1; Fig. 6 a circuit diagram of a reversible-conversion transmitting and receiving equipment in which is mounted the frequency-conversion mixer shown in Fig. 1; and Figs. 7 and 8 circuit diagrams of conventional frequency-conversion mixers. An embodiment of the present invention will now be described in detail with reference to the accompanying drawings. Fig. 1 is a circuit diagram of a frequency-conversion mixer according to an embodiment of the present invention. In the Figures 1-6, symbol J designates an input terminal to which is applied a receiving signal R of a frequency f₁, H an input terminal to which is applied a local-oscillator signal OSC of a frequency f₂, G a common terminal (usually connected to ground), I an output terminal for generating an intermediate frequency signal IF of the frequencies f₁, f₂, f₁ + f₂ and |f₁ - f₂|; D₁, D₂, D₃ and D₄ diodes, and C₁ a capacitor for dc component removing purposes. Fig. 2 shows the relation between the input and output signals in the frequency-conversion mixer shown in Fig. 1. In other words, when the receiving signal R is applied to the terminal J and the local-oscillator signal OSC is applied to the terminal H, the intermediate frequency signal IF is produced from the terminal I. Next, the operation of the frequency-conversion mixer shown in Fig. 1 will be described. In the first place, the local-oscillator signal OSC applied to the terminal H is subjected to non-linear detection by the diodes D₃ and D₄. At this time, the potential at a point P is maintained substantially at a value which is 1/2 of the local-oscillator signal OSC by the diodes D₃ and D₄. The receiving signal R applied to the terminal J is mixed with the local-oscillator signal OSC at the point P through the diodes D₁ and D₂. It is to be noted that the level of the local-oscillator signal OSC is sufficient even if it is below 0 dbm. Further, it is well known that the application of signals of different frequencies to diodes or non-linear detecting elements results in the production of signals of the sum and difference frequencies and will not be described further, therefore. The application of a reverse voltage produces a capacitance component between the cathode and anode of the diode. In the case of the diodes D₁ and D₂ which are connected inversely with respect to each other in the embodiment, the capacitance is on the order of 0.2 to 1 pF. A capacitance of this order is an ideal value for a coupling capacitor in cases where the frequency f₁ is higher than 50 MHz. Therefore, the receiving signal R is not practically attenuated and its passing loss is extremely small. As a result, the present invention has the effect of eliminating the occurrence of the phenomenon that the sensitivity of the ordinary diode mixer is deteriorated due to its dead zone to small signals and matching the impedance of an external circuit connected to the terminal J and the impedance of the point P. The intermediate frequency signal IF generated from the point P has the frequency components of f₁ ,f₂, f₁ + f₂ and |f₁ - f₂|. The capacitor C₁ removes the dc component from the intermediate frequency signal IF and outputs it. Further, in order to obtain the desired frequency f₁ + f₂ or |f₁ - f₂|, a filter 10 for passing the desired frequency component is connected to the terminal I. In this case, a filter with a low impedance input is connected. It is to be noted that while the frequency-conversion mixer according to the present embodiment incorporates the coupling capacitor C₁ to take the form of a one-chip IC, it may also be formed by assembling individual components. Also, the mixer may take the form of a one-chip IC to which, as, for example, a coupling capacitor C₁ of below 50 MHz is externally attached. In addition, the one-chip IC frequency-conversion mixer may be of a modular construction as shown in Fig. 4. By assembling the mixer as a module, there is the effect of making easy its fitting in a receiver as shown in Fig.5. In this case, where it is desired to incorporate the mixer in a receiver of the type employing the conventional diode mixer or double balanced mixer, it can be incorporated as such in place of the diode mixer or the double balanced mixer and it can be directly coupled to the tuning circuits. Where the frequency-conversion mixer according to the present embodiment is mounted, the manufacturing cost of the mixer circuit on the whole is substantially the same as the diode mixer or it is reduced to 1/10 as compared with the double balanced mixer as a single unit in an X-band radar. Further, the outputs of the high frequency amplifier and the local oscillator circuit amplifying unit can be reduced to thereby reduce the cost to substantially about 2/3. Still further, if a signal S of a frequency f₃ is applied to the terminal I instead of applying the receiving signal R of the frequency f₁ to the terminal J as shown in Fig. 6, a signal of a frequency f₂ ± f₃ is generated from the terminal J. In other words, the reversible conversion is permitted between the terminals J and I and the mixer can be applied to a reversible-conversion transmitting and receiving equipment. As mentioned previously, the frequency-conversion mixer in accordance with the present invention is small in size and low in conversion loss and requires no adjustment as compared with the conventional mixers such as the double balanced mixer requiring the use of input-output transformers. It is to be noted that the frequency-conversion mixer according to the present invention can be used in a variety of equipment involving frequencies in the range of the low-frequency to the ultra-short frequency, e.g., as a satellite broadcasting receiver mixer, HF-SHF radio communication/transmitting and receiving mixer, microwave radar mixer, citizen's general radio, FM radio or television receiver mixer, spectrum analyzer mixer, heterodyne-type measuring instrument mixer, phase-locked loop oscillator mixer and phase discriminator. 1 tuning circuit G common terminal (group) 2 diode H input terminal 3 tuning circuit I terminal (input) 10 filter IF intermediate frequency J terminal (for receiving signal) C₁ capacitor, coupling D₁ first diode OSC local oscillator signal D₂ second diode R receiving signal D₃ third diode P point D₄ fourth diode S signal f - frequency T₁ input-output transformer T₂ input-output transformer

Claims: A frequency-conversion mixer comprising: input means for receiving a signal, the input means having a terminal (J) for receiving the signal, a point (P), and first and second oppositely oriented diodes (D1, D2) connected in parallel between the terminal (J) for receiving the signal and the point (P), detecting means having an input terminal (H) for a local oscillator signal, a common terminal (G), and third and fourth diodes (D3, D4) connected in forward series from the common terminal (G) to the input terminal (H) for the local oscillator signal with the point (P) connected between the third and fourth diode (D3, D4), and a dc component removing capacitor (C1) connected to the point (P) and an output terminal (I). A frequency-conversion mixer according to claim 1, wherein said input means and said detecting means are in the form of a one-chip IC. A frequency-conversion mixer according to claim 1, wherein said input means, said detecting means and said capacitor (C1) are in the form of a one-chip IC. A frequency-conversion mixer according to claim 1, wherein a signal of a first frequency is supplied to said input means, and a signal of a second frequency is supplied to said detecting means. A frequency-conversion mixer according to claim 4, wherein a signal of a frequency corresponding to the difference or sum of said first and second frequencies is produced from the output terminal (I). A frequency-conversion mixer according to claim 5, further comprising a filter connected to the output terminal (I) to pass said signal of the requency corresponding to the difference or sum of said first and second frequencies. A frequency-conversion mixer according to claim 1, wherein a signal of a second frequency is supplied to said detecting means and a signal of a third frequency is supplied to an output side of said capacitor whereby a signal of a frequency corresponding to the difference or sum of said second and third frequencies is produced from said input means.

Inventors: SUZUKI EIJI, SUZUKI , EIJI
Applicants: KOKAN DENSETSU KOGYO KABUSHIKI, KOKAN DENSETSU KOGYO KABUSHIKI KAISHA
Application year: 1990
Main classification: H03D7
IPC codes: H03D7