JPH046282B2 - - Google Patents

Description

TECHNICAL FIELD The present invention relates to a pin diode driver circuit, and more particularly to a pin diode driver circuit that improves attenuation control characteristics in a variable attenuator using a pin diode.

(Prior art) Conventionally, for example, in a variable attenuator that adjusts the level of a signal in an intermediate frequency band, a pin diode is used as an attenuation element, and a bias voltage to the pin diode is applied as a voltage for controlling the amount of attenuation. , a method of controlling and adjusting the amount of attenuation is used. FIGS. 1a and 1b show examples of variable attenuation circuits using pin diodes, which are commonly used in the past. In the case of FIG. 1a, the signal input from the terminal 101 is It is attenuated in accordance with the impedance exhibited by ₁ and output from the terminal 103. In this case, the control voltage of a commonly used pin diode driver circuit, which controls the bias voltage of pin diode X ₁ in voltage control mode, is input from terminal 102, and resistors R ₁ and R ₂ are Through pin diode x ₁
A bias voltage corresponding to the control voltage is applied to set a predetermined amount of attenuation. In the case of FIG. 1b, pin diodes X ₂ and X ₃ are connected as attenuating elements so as to have opposite polarities, and terminal 105 is connected to the pin diode driver circuit in voltage control mode. A bias voltage is applied to each pin diode through resistors R ₃ and R ₄ in response to the positive and negative bipolar control voltages input through the first
As in the case of FIG. a, the amount of transmission attenuation between the signal input and output terminals 104 and 105 is set.

FIG. 3a shows an example of attenuation control characteristics in a variable attenuation circuit when attenuation is controlled using a conventional pin diode driver in voltage control mode. In the figure, the horizontal axis shows the control voltage for the pin diode driver, and the vertical axis shows the amount of attenuation in the variable attenuation circuit. Note that when a circuit corresponding to FIG. 1b is used as the variable attenuation circuit, it exhibits attenuation characteristics that are symmetrical with respect to the vertical axis in response to the positive and negative polarities of the control voltage. In FIG. 3a, only the attenuation control characteristics for positive control voltages are shown. As is clear from Fig. 3a, in response to the control voltage input, when the DC bias voltage to the pin diode rises, the attenuation amount for the signal input changes rapidly, and therefore However, due to the above-mentioned attenuation characteristics, the temperature dependence of the attenuation characteristics becomes high, resulting in a decrease in the attenuation control accuracy due to temperature changes. is also involved.

(Object of the Invention) The object of the present invention is to eliminate the above-mentioned drawbacks and change the control drive for the pin diode from the voltage control mode in response to the attenuation control voltage for the variable attenuation circuit using the pin diode as an attenuation element. Attenuation control accuracy for the variable attenuation circuit can be improved by having both the function of converting to the current control mode and the control function of suppressing the control current in the current control mode in a predetermined control voltage range of the attenuation control voltage. The object of the present invention is to provide a pin diode driver circuit that significantly improves the performance.

(Structure of the Invention) The pin diode driver circuit of the present invention includes:
By applying a variable DC bias voltage to the pin diode in response to a predetermined attenuation control voltage,
In a pin diode driver circuit that controls and adjusts transmission attenuation for a predetermined signal, the attenuation control voltage value is adjusted in response to the attenuation control voltage input in order to drive the pin diode in a current mode. It is configured to include a voltage-current conversion circuit that converts into a current value via non-linear characteristics and outputs it as an attenuation amount control current to the pin diode.

(Embodiments of the Invention) Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 2a is a block diagram showing essential parts of an embodiment of the present invention and a corresponding variable attenuation circuit. In the figure, the pin diode driver circuit 3 of the present invention includes differential amplifiers 1 and 2, resistors R ₁₁ , R ₁₂ and a Zener diode X ₅ corresponding to a terminal 109 to which an attenuation control voltage is input. A nonlinear circuit containing and resistors R ₇ to _{R 10} and
It consists of R ₁₃ and a pin diode.
The driver circuit 3 itself forms the voltage-current conversion circuit itself.

In FIG. 2a, differential amplifier 1, resistor R ₇ ,
R ₈ , R ₉ and R ₁₀ form a common mode adder circuit, and the differential amplifier 2 whose output is fed back to the negative phase input side forms a voltage follower circuit. Now, let the attenuation control voltage input from terminal 109 be Vi, set the resistance values of resistors R ₇ , R ₈ , R ₉ and R ₁₀ as R ₇ = R ₈ = R ₉ = R ₁₀ ≡R, and
If _the impedance of the _nonlinear circuit including R ₁₁ , R ₁₂ and _the Zener diode Assuming that the output voltage of amplifier 2 is _V1 , the following equation holds true from the input/output characteristics of the common-mode addition circuit.

V ₀ = Vi + _{V 1} (1) Furthermore, if the impedance of the _variable attenuation circuit including the _{pin diode} Since the input impedance of the voltage follower circuit is infinitely large, the output current I ₀ consistently flows through the impedance _RC of the nonlinear circuit and the impedance _RL . Therefore, a voltage of V ₂ =I ₀ R _L (2) is applied to the positive phase input side of the voltage follower circuit including the differential amplifier 2. However, in a voltage follower circuit where the output voltage is fed back to the negative phase input side, the input and output voltages are equal, so V ₁ =
It becomes V ₂ . Therefore, the following equation can be obtained from equations (1) and (2).

V ₀ = Vi + I ₀ R _L (3) Also, from the relationship between the output voltage V ₀ of the common-mode adder circuit and the output current I ₀ flowing through impedances R _C and R _L , V ₀ = I ₀ (R _C + R _L ) (4) From equations (3) and (4) above, the following equation is given.

I ₀ = Vi/R _C (5) As is clear from equation (5) above, the output current I ₀
is proportional to the attenuation control voltage Vi and inversely proportional to the nonlinear impedance R C, regardless of the value of the impedance R _L created by the parallel connection of the impedance looking into the variable attenuation circuit including the pin diode _{X 4} and the resistor R ₁₃ . are doing. That is, the output current I ₀
is output as a voltage-current exchange value for attenuation control corresponding to the attenuation control voltage Vi, that is, a control current for the variable attenuation circuit. Here, by appropriately selecting the circuit components of the impedance R _C of the nonlinear circuit, it is possible to adjust the value of this control current I ₀ and form a control current control circuit for the variable attenuation circuit.

Also, the impedance R _C is the resistor R ₁₂ and the Zener diode in the case of Figure 2a.
It is formed by the parallel connection of the series impedance _{of X5} and the resistor _R11 , and the relationship between the resistors _R11 and _R12 is selected so that _R11≫R12 , and
By choosing the value of R ₁₁ to a suitable resistance value, the relationship of the control current I ₀ to the control voltage Vi is modified in correspondence with the Zener voltage in the Zener diode X ₅ , and as a result in the variable attenuation circuit. It becomes possible to improve the attenuation control characteristics. That is, in the region where the control voltage Vi for the attenuation amount is low, the bias voltage at the Zener diode X ₅ with respect to the voltage V ₀ is:
is lower than the Zener voltage and therefore the impedance R _C is effectively a resistor since the bypass containing the Zener diode X ₅ is open.
Acts as _R11 . That is, as is clear from equation (5) above, the control current is I ₀ = Vi/R ₁₁ ,
The relationship between the control voltage Vi and the control current I ₀ is the resistor
Defined by the resistance value of _R11 . This means that
By appropriately choosing the resistance value of the resistor R ₁₁ , the bias voltage _of the Zener diode
This means that the Vi-I ₀ characteristic can be set to a desired characteristic in a control voltage range below a predetermined Zener voltage. As the control voltage Vi increases, when the bias voltage for the Zener diode X ₅ exceeds the Zener voltage, the bypass containing the Zener diode X ₅ becomes conductive, and the control current I ₀ flows across the resistor R Apart from being regulated only by _{R 11} , it is regulated by resistor R ₁₂ , and the amount of change with respect to Vi tends to increase.

The control current I ₀ is, in principle, connected to the impedance R _C with a resistor R ₁₃ , a resistor R ₅ in a variable attenuation circuit, a pin diode X ₄ and a resistor
Uniquely, the control voltage Vi and the impedance R _C , regardless of the impedance of the load circuit, including R ₆ and
This is the current value determined by the control current _I0 , and the bias voltage of the pin _diode be done. Therefore, it is input from the terminal 109 of the pin diode driver circuit 3. The attenuation control characteristic corresponding to the control voltage Vi for the attenuation amount is as shown in FIG. 3b,
In the range of O to Vb of control voltage Vi, the characteristic is almost linear, and with voltage Vb as the boundary point, Vi
transition to a characteristic in which the rate of change with respect to increases. Needless to say, the aforementioned voltage value Vb corresponds to the control voltage at which the bias voltage at the Zener diode X ₅ reaches the predetermined Zener voltage.

As is clear from a comparison of FIGS. 3a and 3b, when using the pin diode driver circuit of the present invention, the attenuation control characteristic corresponding to the control voltage Vi is from Vi=O to Vb. As mentioned above, in the region where Vi exceeds Vb, it is regulated by resistor R ₁₁ and the characteristic is improved to a low slope, and in the region where Vi exceeds Vb, it is regulated by resistor R ₁₂ and the characteristic is improved to a relatively steep slope. I can see it moving. Therefore, in order to improve the change in attenuation amount corresponding to the input of the control voltage Vi to a low slope characteristic, the amount of change in attenuation amount ΔL corresponding to the amount of change ΔVi in Vi is made a relatively small amount. Since the value of △Vi/△L can be increased, the attenuation amount control accuracy for the variable attenuation circuit corresponding to the control voltage Vi is improved in proportion to the value of △Vi/△L. be able to. As mentioned above, even in the control voltage region where Vi exceeds Vb, as shown in Figure 3b, although the value of △Vi/△L tends to increase, the resistance value of resistor _R12 By selecting
The effective range of the control voltage Vi can be expanded without significantly deteriorating the attenuation control accuracy.
In addition, with the improvement of the value of △Vi/△L,
The dependence on temperature conditions is also reduced, and the temperature characteristics of attenuation control accuracy are also improved.

FIG. 2b is a block diagram showing the main parts of another embodiment of the present invention and a corresponding variable attenuation circuit. In the figure, the pin diode driver circuit 6 of the present invention includes differential amplifiers 4 and 5, resistors R ₂₀ , R ₂₁ , and diodes X ₈ , X ₉ corresponding to the terminal 112 to which the attenuation control voltage is input. It consists of a nonlinear circuit including Zener diodes X ₁₀ and X ₁₁ , and resistors R ₁₆ to R ₁₅ and R ₂₂ , and a pin diode driver circuit 6.
itself forms the voltage-current conversion circuit itself.

The difference between the embodiment shown in FIG. 2b and the embodiment shown in FIG. 2a is that the pin diode driver circuit is included in the nonlinear circuit, which is the main component of the control current control circuit. The semiconductor circuit element is not composed of a single Zener diode, but is connected in series with diodes X ₈ and X ₉ , which are also connected in series with mutually opposite polarities. Zener to be
The diodes _X10 and _X11 are connected in parallel, and in the corresponding variable attenuation circuit, as in the case of Fig. 1b,
Two pin diodes are connected with opposite polarity and used as attenuation elements. The operation of the variable attenuation circuit using two pin diodes has already been mentioned in the description of the conventional example shown in FIG. 1b. For the operation of the pin diode driver circuit shown in Figure 2b, the resistor forming the control current control circuit
The attenuation control characteristics are basically as shown in Figure 3b, with only differences due to the different circuit configurations of R ₂₁ , diodes X ₈ and X ₉ , and Zener diodes X ₁₀ and X ₁₁ . The improvements made in this case are exactly the same as in the case of FIG. 2a.
In Figure 2b, the Zener diodes X ₁₀ and X ₁₁ are connected in series with the diodes X ₈ and X ₉ , respectively, with opposite polarity because the control voltage Vi input from terminal 112 is positive. In the region of , the arm consisting of _the diode X ₈ and _the Zener diode
When the control voltage Vi is in the negative region, the arm consisting of diode X ₉ and Zener diode X ₁₁ controls the control current.
It acts to control I ₀ . Of course, the control voltage Vi
It goes without saying that the positive and negative polarities in correspond to the two pin diodes X ₆ and X ₇ in the variable attenuation circuit, respectively.
In the case of the embodiment shown in FIG. 2b, the attenuation amount control characteristics shown in FIG. It is stipulated in a joint manner.

(Effects of the Invention) As described above in detail, the present invention performs control drive for the pin diode forming the attenuation element of the variable attenuator in the current mode, and suppresses and controls the control current in the current mode. This has the effect that the attenuation control accuracy corresponding to the control voltage can be significantly improved, and the temperature characteristics of the attenuation control accuracy can also be improved.

[Brief explanation of drawings]

1A and 1B are block diagrams showing the main parts of a variable attenuation circuit, and FIGS. 2A and 2B are block diagrams showing the main parts of two examples of variable attenuation circuits corresponding to an embodiment of the present invention. 3A and 3B are diagrams showing attenuation control characteristics, respectively. In the figure, 1, 2, 4, 5...differential amplifiers.

Claims (1)

[Claims] 1 In a pin diode driver circuit that controls and adjusts the transmission attenuation for a predetermined signal by applying a variable DC bias voltage to the pin diode in response to a predetermined attenuation control voltage, Then, in order to perform control drive for the pin diode in current mode, the attenuation control voltage value is converted into a current value via non-linear characteristics, and the voltage-current conversion is outputted as an attenuation control current for the pin diode. A pin diode driver circuit characterized by comprising a circuit.