JPH0412050B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switch circuit for switching input signals such as carrier waves or modulated waves.

Time division communication method and SCPC (Single channel per
In the carrier type, a burst output signal is generated by switching a carrier wave or a modulated wave in an IF (intermediate frequency) band or an RF (radio frequency) band. Conventionally, however, such switching has normally been performed by a switch circuit that uses a PIN diode and performs switching by utilizing resistance changes caused by turning on and off the PIN diode.

FIG. 1 shows the configuration of a typical conventional switch circuit.

In the same figure, the on/off signal for bursting the input signal IF or RF signal is gate 1.
The signal is then added to a time constant circuit (integrator circuit) consisting of a resistor 2 and a capacitor 3. The output of the time constant circuit is applied to the PIN diode 5 via the choke coil 4, thereby causing a diode current to flow.
The resistance of the PIN diode 5 is very large, close to infinity in the off state, but extremely small and almost zero in the on state. Therefore, when the PIN diode 5 is off, the input signal is transferred to the capacitor 6,
However, when the PIN diode 5 is on, no output signal is generated. In this way, a burst signal output can be obtained by the circuit of FIG. In FIG. 1, the chiyoke coil 4,
The PIN diode 5 and capacitors 6 and 7 constitute a switch section 8. Further, although in FIG. 1 the connectors are connected in parallel to the signal, the same effect can be obtained even if the connectors are inserted in series with the signal.

In the circuit shown in Figure 1, resistor 2 and capacitor 3
If there is no time constant circuit, the switching of the input signal is performed according to the on/off signal waveform consisting of a rectangular wave as shown in FIG. 2a. In such a state, pulses based on the instantaneous response occur at the leading and trailing edges of the burst signal output, thereby generating unnecessary waves. For this reason, by using a time constant circuit consisting of a resistor 2 and a capacitor 3, the rise and fall of the diode current are made gentler and the generation of unnecessary waves is prevented.

However, when the PIN diode turns on, it responds at high speed due to its positive characteristics, so a current response waveform with a time constant approximately equal to the time constant of the time constant circuit consisting of resistor 2 and capacitor 3 is obtained. When turned off, the charge accumulated in the capacitance of the PIN diode is discharged, so the response waveform generally becomes longer than the response determined by the time constant τ.

However, it is desirable that the time constants shaped by the rising and falling waveforms of the on/off signal in the switch circuit be equal.

FIG. 2 shows waveforms of signals at various parts in the switch circuit of FIG. 1. In the figure, a indicates the waveform of an on/off signal applied for switching. b shows an output waveform of a time constant circuit consisting of a resistor 2 and a capacitor 3, and a transient response with a time constant τ occurs at rise and fall. c is
The current response waveform of the PIN diode 5 is shown, and the time constant τ _A when turned on is almost equal to the time constant τ of the time constant circuit, but the time constant τ _B when turned off is longer than the time constant τ. In other words, the relationship is ττ _A < τ _B. d shows the waveform of the burst signal output, the rise of which is slower than the fall.

In this way, it is undesirable from the viewpoint of maintaining signal quality that the amplitude change characteristics of the burst signal are affected based on the response of the switching diode. Conventionally, therefore, a method has been used to shorten the discharge time by applying a reverse voltage to the diode when it is turned off.

FIG. 3 shows the configuration of a driver circuit that prevents the influence of accumulated charge in the diode. In the same figure, in response to the on/off signal that causes current to flow through the PIN diode, when the diode is turned on, a positive voltage +Va is output, and when it is turned off, a negative voltage -Va is output.
Switch and output. The output of the switch 9 is supplied to the switch section 8 shown in FIG. 1 through a time constant circuit consisting of a resistor 2 and a capacitor 3 (see FIG. 1). Therefore, when the PIN diode 5 is turned off, its charge causes a reverse current to flow, shortening the discharge time.

FIG. 4 shows a current response waveform when the driver circuit shown in FIG. 3 is used. In the driver circuit shown in Figure 3, a reverse voltage is applied to shorten the discharge time of the diode charge, so the time constant of the current response waveform when turning off is τ _c , and in the case of Figure 2, It has been shortened in comparison.

However, even when using the driver circuit shown in FIG. 3, the effect is not sufficient when the time constant of the time constant circuit is large. That is, since discharge is performed according to a time constant determined by the resistance of the time constant circuit and the capacitance of the PIN diode, there is a drawback that the discharge time becomes longer when the resistance value is large.

As an improvement measure for the above problem, as _shown in FIG.
A method in which 1 is the time constant has been considered and good results have been obtained. (R ₁ R') In FIG. 5, when the PIN diode 5 is controlled with a switching waveform having a positive voltage +V and a negative voltage -V as shown in FIG. The waveform shown in Figure f is obtained. Waveform f-1 (rising), f-
2 (falling) is a waveform shaped by resistor 2 and capacitor 3 (time constant R ₁ · C ₁ ), and is a falling waveform f
The reason why the time constant τf-2 of -2 is larger than the rising time constant τf-1 is because the capacitance of the diode 5 is added to the time constant.

With diode 5 connected, when the discharge voltage of capacitor (C ₁ ) 3 and diode 5 exceeds 0 volts (0V) 13 and becomes a negative voltage, diode D'1
0 operates, the falling characteristic becomes steep and the waveform f-3
is shaped, and the time constant becomes Δt. Therefore, the falling time constant is τf-3. In this case, the diode
It becomes faster by the time when D'10 becomes reverse conductive, and before that, the discharge time by the PIN diode 5 becomes dominant, and the resistance (R ₁ ) 2 and capacitor (C ₁ ) 3 with the desired time constant becomes faster. difficult to obtain.

In view of the above-mentioned drawbacks of the conventional example, the present invention provides a new switch circuit in which the falling waveform of the on/off signal for switching is shaped by a differentiating circuit to equalize the time constants of the rise and fall of the burst signal. The purpose is to

The above purpose is to provide a PIN diode for switching to turn on/off a burst signal, a gate to output a square wave on/off signal for switching, a buffer amplifier to supply current to the PIN diode, and an output of the gate. an integrating circuit comprising a first resistor connected between the input terminal of the buffer amplifier and the input terminal of the buffer amplifier, and a first capacitor connected between the input terminal of the buffer amplifier and the ground; A differential circuit is connected in series with a resistor, the second capacitor is connected to the output terminal of the gate, and the second resistor is connected to the ground, and the buffer amplifier has a cathode at the midpoint of the series connection. This is achieved by a switch circuit characterized in that it has control diodes each having an anode connected to its input terminal.

The present invention will be described below based on the embodiment shown in FIG. 7, and the on/off signal waveforms, switching waveforms, etc. shown in FIG.

In Figure 7, the PIN output from gate 1
The on/off signal (Fig. 8g) for switching the diode 5 is a time constant circuit (integrator circuit) composed of a resistor (R ₁ ) 2 and a capacitor (C ₁ ) 3, as shown in Fig. 8h. It is formatted like this. The rising and falling waveforms of waveform h and the time constants of h-1 and h-2 are equal. Falling waveform g of the on/off signal g
-1 is connected to the resistor (R ₂ ) through the diode D'10.
14 and a capacitor (C ₂ ) 15, the waveforms h and i are combined at the output point 16 to form a waveform j.

The waveform j is inputted to the switching unit 8 via the buffer amplifier 17, and is inputted via the switch coil 4.
By switching the PIN diode 5, the waveform j is shaped by the capacitance of the diode 5 into a burst signal waveform k in which the time constants of the rising waveform k-1 and the falling waveform k-2 are almost equal, as shown in FIG. 8k. .

FIG. 9 shows an application example of the present invention, in which the embodiment of the present invention is connected to a first circuit 18, and the conventional example shown in FIG. 5 is connected to a second circuit 19 via a buffer amplifier 12. However, the time constant of the resistance capacitor should be set appropriately.

In the figure, the on/off waveform shown in FIG. 8g is the time constant resistance (R _1-1 ) of the integrating circuit of the first circuit 18
20, the shaped waveform is shaped by the capacitor (C _1-1 ) 21, the time constant resistor (R ₂ ) 14 of the differentiator circuit, and the capacitor (C ₂ ) 15, and the shaped waveform is approximately as shown in FIG. j is input to the second circuit 19 via the buffer amplifier 12 which uses positive and negative voltages, and in the second circuit 19, the waveform is changed to the one shown in FIG. 8k by the circuit operation shown in FIG. The rising waveform and the falling waveform are shaped into a burst signal with equal time constants.

As described above, the present invention has the advantage that the rise and fall waveforms of the burst signal can be made equal by adding a differentiating circuit with a simple circuit configuration to the switch circuit.

[Brief explanation of drawings]

Figures 1 and 5 show conventional switch circuits,
The figure shows the waveform at each point in Figure 1, Figure 3 shows the influence of negative voltage on the time constant, Figure 4 shows the waveform created by Figure 3, and Figure 6 shows the waveform in Figure 5. The waveforms thus created, FIG. 7 is an embodiment of the present invention, and FIG.
The waveforms at each point in the figure, FIG. 9, show an application example of the present invention. In the figure, 1 is a gate, 2, 14, 20, 22 are resistors, 3, 6, 7, 15, 21, 23 are capacitors, 4 is a chiyoke coil, 5 is a PIN diode,
8 is a switch section, 9 is a switch that outputs a positive voltage -Va, 10, 10-1, 10-2 are diodes, 11, 11-1, 11-2 are operating resistances of the diodes, 12, 17 are buffer amplifiers, 13 is 0
Volt level, 16 is the output point, 18 is the first circuit,
19 indicates a second circuit.

Claims (1)

[Claims] 1. A PIN diode for switching to turn on/off the burst signal, a gate to output a square wave on/off signal for switching, and
a buffer amplifier that supplies current to the PIN diode; a first resistor connected between the output end of the gate and the input end of the buffer amplifier; and a first capacitor connected between the input end of the buffer amplifier and ground. and a differential circuit comprising an integrating circuit consisting of a second capacitor and a second resistor connected in series, the second capacitor being connected to the output terminal of the gate, and the second resistor being connected to the ground. and,
A switch circuit comprising a control diode having a cathode connected to the middle point of the series connection and a control diode having an anode connected to the input terminal of the buffer amplifier.