JP5116714B2 - High frequency mixer - Google Patents

Description

  The present invention is used for a high-frequency mixer, particularly a receiver such as a sensor or a radar used in a high-frequency band, and relates to a circuit configuration for ensuring stable operation.

  In general, in a sensor or radar system used in the microwave band or the millimeter wave band, a high-frequency mixer is used in a receiving circuit thereof. In this high-frequency mixer, a part of a transmission signal is a local signal (LO signal). ), And an intermediate frequency signal (IF signal) as a frequency difference component is formed by mixing with the received signal (RF signal). As this high-frequency mixer, for example, the single balanced mixer of FIG. 8 using a rat race line is used, and the circuit shown in FIG. 9 is configured.

  8 and 9, the single balanced mixer includes a rat race line 7 in which a first diode (Dx1) 5 and a second diode (Dx2) 6 made of a Schottky barrier diode (SBD) are made of a 1.5λ line. The LO port 8 is connected to the first port a, the RF end 9 is connected to the third port c, and the output side of the first diode 5 and the second diode 6 is connected to the fourth port d and the second port b. The IF output terminal 10 is connected.

According to such a configuration of the high frequency mixer, the local oscillation signal input from the LO end 8 is L = 2 cos (ω _Lt + θ _L ), and the reception signal input from the RF end 9 is R = 2 cos (ω _Rt + Θ _R ), the signals (Dx1-in, Dx2-in) at the input ends of the first diode 5 and the second diode 6 are as shown in FIG.
Dx1-in: L = cos (ω _Lt + (θ _L + (π / 2))),
R = cos (ω _Rt + (θ _R − (π / 2))) (1)
Dx2-in: L = cos (ω _Lt + (θ _L − (π / 2))),
R = cos (ω _Rt + (θ _R − (π / 2))) (2)
And
The outputs (Dx1-out, Dx2-out) of the first diode 5 and the second diode 6 and the output (IFout) from the IF output terminal 10 are
Dx1-out: -cos (([omega] _{L- [} omega] _R ) t + ([theta] _{L- [} theta] _R + [pi])) (3)
Dx2-out: + cos (([omega] _{L- [} omega] _R ) t + ([theta] _{L- [} theta] _R )) (4)
IFout: Dx1-out + Dx2-out
= −cos ((ω _L −ω _R ) t + (θ _L −θ _R + π)) + cos ((ω _L −ω _R ) t + (θ _L −θ _R ))
= Cos (([omega] _{L- [} omega] _R ) t + ([theta] _{L- [} theta] _R )) + cos (([omega] _{L- [} omega] _R ) t + ([theta] _{L- [} theta] _R )))
= 2 × cos ((ω _L −ω _R ) t + (θ _L −θ _R )) (5)
It becomes.

  In this high-frequency mixer, since the peripheral circuit of the first diode (Dx1) 5 and the second diode (Dx2) 6 does not have a capacitance component (capacitor), the IF signal operates from DC (direct current). (LO) When the first diode 5 and the second diode 6 are sufficiently biased by the signal power, the conversion loss characteristic is good as a high frequency mixer (ratio of the received signal power from the RF end and the intermediate frequency signal power). Is obtained.

Japanese Examined Patent Publication No. 54-029218

  However, in the conventional high-frequency mixer of FIGS. 8 and 9, if the local signal power for biasing the first diode 5 and the second diode 6 made of SBD to the nonlinear region is insufficient (decreased), the conversion loss of the high-frequency mixer However, the conversion loss is highly dependent on the local signal power.

  FIG. 10 shows the change in conversion loss with respect to the local oscillation signal power in the conventional high frequency mixer. As shown in the characteristic 501 in the figure, in the range where the local oscillation signal power is insufficient at −2 dBm or less. It can be seen that the value of the conversion loss is reduced.

  The present invention has been made in view of the above problems, and its purpose is to perform a stable operation in which conversion efficiency is difficult to decrease even when the local signal power is insufficient, and even when the ambient temperature fluctuates, An object of the present invention is to provide a high-frequency mixer that can ensure stable operation.

In order to achieve the above object, the invention according to claim 1 includes a rat race circuit in which a received signal input terminal, a local signal input terminal, a cathode of a first diode, and an anode of a second diode are connected to different ports. In a high frequency mixer in which an intermediate frequency signal output terminal is connected between a port to which the reception signal input terminal is connected and a port to which the first diode is connected, to the first diode and the second diode An external positive power source for applying a bias voltage, a first resistor connected between the external positive power source and the anode of the first diode, and a second resistor connected between the anode of the first diode and the ground And the same parallel resistance as when the first resistor and the second resistor are connected in parallel, or the first resistor and the second resistor are connected in parallel. Third resistor equivalent to continue the resistance component, characterized in that the provided.
Invention comprises received signal input terminals, the local oscillator signal input, a rat race circuit anodes are connected to different ports of the cathode and a second diode of the first diode, the reception signal input terminal according to claim 2 An external positive power supply for applying a bias voltage to the first diode and the second diode in a high frequency mixer to which an intermediate frequency signal output terminal is connected between a port connected to the first diode and a port connected to the first diode; A first resistor connected between the external positive power source and the anode of the first diode; a first temperature variable resistor connected between the anode of the first diode and the ground; and the second diode. A fourth resistor connected between the cathode of the first and the ground and having a value equal to the value of the first resistor, and a fourth temperature variable connected in parallel with the fourth resistor and having a value equal to the value of the first temperature variable resistor. Characterized by providing anti and, a.

  According to the configuration of the first aspect, the intermediate frequency (IF) signal operates from DC, and only the external positive power source (the power source that does not require a negative power source for the external power source) is used. By biasing the second diode in a non-linear region, that is, by forcibly applying a bias current, a decrease in conversion efficiency of the high-frequency mixer can be reduced even when the local signal power is insufficient. That is, by providing an external positive power source, connecting the first resistor to the external positive power source as viewed from the anode of the first diode, and connecting the second resistor to the ground, the local signal power Even when the voltage drops, the voltage between the anode and the cathode of the first diode and the voltage between the anode and the cathode of the second diode can be kept high, and as a result, the conversion efficiency is improved.

  On the other hand, in the above configuration, when the ambient temperature changes, even if the voltage of the external positive power supply is constant, the bias currents of the first diode and the second diode decrease at a low temperature and increase at a high temperature.

  In order to solve this problem, in the configuration of claim 2, one of the second resistor on the ground side and the parallel resistor is replaced with the first and fourth temperature variable resistors. Due to the arrangement of the variable resistors, the bias currents of the first diode and the second diode are kept constant even when the ambient temperature varies. That is, the resistance value of the temperature variable resistor arranged on the ground side increases at a low temperature and decreases at a high temperature, so that the bias current for the first and second diodes becomes constant, and is not affected by fluctuations in the ambient temperature. Operation is possible.

According to the first aspect of the present invention, in a high-frequency mixer using a rat race circuit, for example, a single balanced mixer, even when the local signal power is insufficient, the reduction in conversion efficiency of the high-frequency mixer can be reduced, and the station with conversion loss The dependence on the generated signal power is reduced, and there is an effect that a stable mixer operation can be ensured.
According to the invention of claim 2, in the high frequency mixer using the rat race circuit, even when the ambient temperature fluctuates, the high frequency mixer is maintained by maintaining the bias current constant by the first and fourth temperature variable resistors. This has the effect of suppressing fluctuations in conversion loss.

It is a circuit diagram which shows the structure of the high frequency mixer which concerns on 1st Example of this invention. It is a graph which shows the change of the anode-cathode voltage of the 1st diode with respect to the local oscillation signal power of the high frequency mixer of 1st Example. It is a graph which shows the conversion loss characteristic (change of the conversion loss with respect to local oscillation signal power) of the high frequency mixer of 1st Example. It is a graph which shows the conversion loss characteristic when ambient temperature fluctuates in the high frequency mixer of 1st Example. It is a graph which shows the current characteristic (change of the forward current with respect to a forward voltage) when ambient temperature fluctuates with a general diode. It is a circuit diagram which shows the structure of the high frequency mixer which concerns on 2nd Example. It is a graph which shows the conversion loss characteristic when ambient temperature fluctuates in the high frequency mixer of 2nd Example. It is a figure which shows the structure and phase relationship of the conventional high frequency mixer (single balanced mixer). It is a circuit diagram which shows the structure of the conventional high frequency mixer. It is a graph which shows the conversion loss characteristic of the conventional high frequency mixer.

  FIG. 1 shows the configuration of a high-frequency mixer (single balanced mixer) according to a first embodiment of the present invention. In the first embodiment, a first diode (SBD) composed of a Schottky barrier diode (SBD) is shown. Dx1) 5 and a second diode (Dx2) 6, having a rat race line 7 composed of a 1.5λ line, the first diode 5 at the fourth port d of the rat race line 7 and the second diode at the fourth port b. 6 is connected. Further, the LO terminal (local signal input terminal) 8 is connected to the first port a of the rat race line 7, and the RF terminal (reception signal input terminal) 9 is connected to the third port c.

An external positive power source 1 is provided to apply a bias voltage (drive voltage) Vop to the first diode 5 and the second diode 6, and the first positive electrode 1 is connected between the external positive power source 1 and the anode of the first diode 5. 1 resistor (resistance value R ₁ ) 2 is connected, and a second resistor (resistance value R ₂ ) 3 is connected between the anode of the first diode 5 and the ground, and the cathode of the second diode and the ground Is connected to a third resistor 4 equal to the resistance component [resistance value R ₃ {= R ₁ · R ₂ / (R ₁ + R ₂ )}] in which the first resistor 2 and the second resistor 3 are connected in parallel. The Incidentally, as shown in parentheses in FIG. 1, it may be connected with equal resistances 2e and the resistance value R ₁ of the first resistor 2, the resistance value R ₂ is equal to the resistance 3e of the second resistor 3 in parallel.

  In the first embodiment, the IF output terminal 10 is connected to a line between the third port c and the fourth port d of the rat race line 7. That is, since the voltage on the cathode (rat race line 7) side of the first diode 5 is higher than that on the anode side, the IF output terminal 10 is arranged on the rat race line 7 side so that the IF signal can be output efficiently. .

  The first embodiment is configured as described above. In the high-frequency mixer circuit shown in FIG. 1, a bias current is forcibly applied to the first diode 5 and the second diode 6 by applying a bias voltage Vop from the external positive power source 1. As a result, the first diode 5 and the second diode 6 are biased in the non-linear region, and even when the local oscillation signal voltage is insufficient, the reduction in conversion efficiency can be reduced.

  FIG. 2 shows the change of the anode-cathode voltage Vak of the first diode 5 with respect to the local signal power. In the conventional circuit, when the local signal power is insufficient as indicated by the dotted line 101, the anode -The cathode voltage Vak is lowered. On the other hand, in the first embodiment, by providing the first resistor 2 and the second resistor 3 together with the external positive power source 1, even when the local signal power is insufficient as shown by the solid line 102, the first diode 5 Thus, the anode-cathode voltage Vak of (and the second diode 6) is kept high, thereby improving the conversion efficiency and obtaining an IF signal (intermediate frequency signal) having a good amplitude.

  Also in this first embodiment, since the peripheral circuit of the first diode 5 and the second diode 6 has no capacitance component (capacitor), the IF signal operates from DC (direct current) as in the conventional circuit. Further, since the input impedance of the external positive power source 1 is low, the impedance is equivalent to the ground for the IF signal, and the first resistor 2 and the second resistor 3 are provided between the first diode 5 and the external positive power source 1. Since the third resistor 4 (or parallel resistors 2e and 3e) identical to the first resistor 2 and the second resistor 3 is also provided between the second diode 6 and the ground, IF In the signal, the impedance when the anode side is viewed from the cathode of the first diode 5 is equal to the impedance when the anode side is viewed from the cathode of the second diode 6. Accordingly, since the impedance balance is maintained, the high-frequency single balanced mixer operates satisfactorily in which noise generated from the first diode 5 and the second diode 6 is canceled.

  FIG. 3 shows the conversion loss characteristic of the first embodiment. Compared with the characteristic 501 of the conventional circuit of FIG. 10, even in a range where the local signal power is insufficient, as in the characteristic 201 of FIG. Then, there is little deterioration of conversion loss (loss value reduction), and stable characteristics with little dependence on fluctuations in local signal power are obtained.

  When the local signal power is sufficient, there is a slight decrease in the conversion loss value compared to the conventional circuit. This decrease is due to the IF signal power being slightly smaller than the resistance of the second resistor 3 and the third resistor 4. Results from being absorbed into the body. However, the conversion loss value does not change greatly with respect to fluctuations in the local oscillation signal power, and the effect of the present invention that provides stable characteristics exceeds the above demerits.

  By the way, in such a configuration of the first embodiment, when the ambient temperature largely fluctuates, there is a disadvantage that the dependence of the local signal power on the conversion loss changes. The configuration of the second embodiment can be employed.

  FIG. 4 shows the conversion loss characteristic when the ambient temperature fluctuates in the configuration of FIG. 1. Compared to the characteristic 201 at normal temperature (+ 25 ° C.), the ambient temperature ( When T) is as low as −50 ° C., the conversion loss (dependence on the local signal power) deteriorates when the local signal power is insufficient, and the conversion loss occurs when the local signal power is sufficient. Improve (the absolute value of conversion loss decreases). On the contrary, as shown in the characteristic 203, when the ambient temperature (T) is as high as + 85 ° C., the behavior is opposite to the above.

  When the ambient temperature fluctuates as described above, the behavior of conversion loss when the local signal power is insufficient is that the voltage Vop of the external positive power supply 1 is constant (the voltage applied to the anode end of the first diode 5 is Even if it is constant, the bias current of the first diode 5 and the second diode 6 is lowered from the normal temperature at a low temperature and increased at a high temperature. FIG. 5 shows current characteristics (change in forward current If with respect to forward voltage Vf) when the ambient temperature varies with a general diode. The ambient temperature in FIG. 5 is normal temperature (+ 25 ° C.). The behavior of the conversion loss in the high-frequency mixer can also be understood from the behavior of the characteristic 302 at low temperature (−50 ° C.) and the characteristic 303 at high temperature (+ 85 ° C.) with respect to the characteristic 301 of FIG. On the other hand, the behavior of the above-described conversion loss when the local signal power is sufficient is that the frequency conversion efficiency of the mixer (SBD) increases at low temperatures, whereas the frequency conversion efficiency decreases at high temperatures.

FIG. 6 shows the configuration of the second embodiment. The basic configuration of the second embodiment is the same as that of FIG. 1, and the first diode 5 is connected to the anode of the first diode (Dx1) 5. And an external positive power source 1 for applying a bias voltage (Vop) to the second diode (Dx2) 6. A first resistor (resistance value R ₁ ) 11 is connected between the external positive power source 1 and the anode of the first diode 5, and a first temperature is connected between the anode of the first diode 5 and the ground. A variable resistor (resistance value RT ₁ ) 12 is connected, and a fourth resistor 13 having a resistance value R ₁ equal to the first resistor 11 and the first temperature variable resistor 12 are connected between the cathode of the second diode 6 and the ground. A fourth temperature variable resistor 14 having a resistance value RT ₁ equal to is connected in parallel.

According to the second embodiment, since the resistance value RT ₁ of the first and fourth temperature variable resistor 12 and 14 at a low temperature is increased, the voltage applied to the anode of the first diode (Dx1) 5 is normal temperature (+ 25 ° C.) increases as compared with, since at high temperatures the reverse is the resistance value RT ₁ of the first and fourth temperature variable resistor 12 decreases, decreases as compared to the normal temperature. Thus, as can be understood from the behavior of the forward current characteristic with respect to the forward voltage of the general diode shown in FIG. 5 at each ambient temperature, even when the ambient temperature fluctuates, the first diode 5 and the first diode 5 The bias current of the two diodes 6 is kept constant, and the deterioration of conversion loss when the local signal power is insufficient is improved.

  In the high frequency mixer of the second embodiment, the IF signal is absorbed in a minute amount by the resistance between the anode of the first diode 5 and the ground and the resistance between the cathode of the second diode and the ground, as in the first embodiment. When the resistance component increases, the conversion loss value increases. Conversely, when the resistance component decreases, the conversion loss value decreases. In contrast to this decrease, in the second embodiment, the first and fourth temperature variable resistors 12 and 14 increase at low temperatures, so that the conversion loss value (conversion efficiency) decreases, and conversely the conversion loss value increases at high temperatures. . Therefore, the behavior of the conversion loss when the local signal power is sufficient when the ambient temperature fluctuates, that is, the phenomenon that the conversion loss value increases at a low temperature and the conversion loss value decreases at a high temperature (FIG. 4) is corrected. The

  FIG. 7 shows the conversion loss characteristics of the second embodiment, which are 401 (normal temperature: + 25 ° C.), 402 (low temperature: −50 ° C.), and 403 (high temperature: + 85 ° C.) of FIG. As in the characteristics, even when the local signal power fluctuates and the ambient temperature changes, the conversion loss decreases and fluctuates little, and a stable characteristic is obtained even when compared with FIG.

  In each of the above embodiments, the 180 ° rat race track 7 is used as the balun, but the same effect can be obtained even if a 90 ° 3 dB branch line coupler or the like is used.

1 ... external positive power supply, 2,11 ... first resistor _(R 1),
2e, 3e ... parallel resistor, 3 ... second resistor _(R 2),
4 ... the third resistor _(R 3), 5 ... first diode,
6 ... 2nd diode, 7 ... Rat race track,
8 ... LO (local signal) end, 9 ... RF (received signal) end,
10 ... IF (intermediate frequency signal) output terminal, 12 ... first temperature variable resistor (RT ₁ ),
13 ... fourth resistor _(R 1), 14 ... fourth temperature variable resistor _(RT 1).

Claims (2)

Received signal input terminal, the local oscillator signal input has a rat race circuit anode of the cathode and the second diode are connected to different ports of the first diode, port and the first of the received signal input connected In a high frequency mixer in which an intermediate frequency signal output terminal is connected between a port to which one diode is connected ,
An external positive power supply for providing a bias voltage to the first diode and the second diode;
A first resistor connected between the external positive power source and the anode of the first diode;
A second resistor connected between the anode of the first diode and ground;
A resistance component connected between the cathode of the second diode and the ground, and the same parallel resistance as when the first resistance and the second resistance are connected in parallel or the first resistance and the second resistance connected in parallel And a third resistor equal to the high-frequency mixer. Received signal input terminal, the local oscillator signal input has a rat race circuit anode of the cathode and the second diode are connected to different ports of the first diode, port and the first of the received signal input connected In a high frequency mixer in which an intermediate frequency signal output terminal is connected between a port to which one diode is connected ,
An external positive power supply for providing a bias voltage to the first diode and the second diode;
A first resistor connected between the external positive power source and the anode of the first diode;
A first temperature variable resistor connected between the anode of the first diode and ground;
A fourth resistor connected between the cathode of the second diode and ground and having a value equal to the value of the first resistor;
A high frequency mixer comprising: a fourth temperature variable resistor connected in parallel with the fourth resistor and having a value equal to the value of the first temperature variable resistor.

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