JPH03190413A - Voltage controlled oscillator - Google Patents

Abstract

PURPOSE:To make the oscillating frequency wide by applying a voltage bringing a 1st varactor into a reverse bias state externally via a 2nd terminal and an RF blocking resistor circuit, and also a 2nd varactor. CONSTITUTION:When capacitors C5, C6 are connected in series with frequency adjustment varactors D1, D2 respectively and a reference voltage is applied to the varactors D1, D2 via reference voltage supply terminals 14, 15 and RF blocking resistors R4, R5 with a sufficiently high resistance to keep the reverse bias state of the varactors D1, D2. Moreover, 2nd varactors D3, D4 in the reverse bias state are connected in parallel with inductors L1, L2 via capacitors C3, C4 with a control voltage applied externally through control voltage supply terminals 12, 13 and RF blocking resistors R2, R3 with a sufficiently high resistance. Thus, the oscillation at a broad band is attained while the modulation sensitivity of an oscillator is suppressed even at an oscillating frequency over the X band.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a voltage controlled oscillator, and more particularly to a variable circuit for excavating frequency of an unstable multivibrator using a varactor as an oscillation frequency adjusting element.

[Conventional technology]

A conventional MMIC voltage controlled oscillator in this building is shown in the circuit diagram of FIG. This circuit uses GaA for oscillation.
s F E T Qt , Q2, a capacitor (or a varactor in a reverse bias state) (, A control voltage VCONT 1 is applied from the outside through the RF blocking resistor R1, resulting in a reverse bias state. The oscillation frequency can be controlled by changing the junction capacitance determined by the reverse bias voltage value.

Here, FET Qs is a current source FET for oscillation FETs Qt and Qh, and buffer amplifiers 1 and 2 receive the positive phase and negative phase outputs of the unstable multivibrator, respectively, and the outputs are sent to output terminals 16 and 17, respectively. Output. In addition, the power supply for each circuit is such that the positive power supply VDD is supplied through the positive power supply terminals 18 and 19, and the negative 'RE' is supplied through the negative '1 source supply terminal 6.
A source Vss is supplied.

In addition, this MMIC-based voltage control voltage control oscillator, divider, phase comparator, reference frequency oscillator using a crystal, low-pass filter, or in combination with a phase-lock-loose (PLL) IC in which these are integrated The phase-lock-loose (PLL) f is used to stabilize the frequency.

Next, the results of computer simulation of the relationship between each element value and the oscillation frequency of the circuit shown in Figure 2 will be explained.

FIG. 3 is a graph showing the relationship between the reverse bias voltage and the junction capacitance of the frequency a4 adjusting varactors (Dl, D2) used in this simulation. The figure shows an active layer formed by ion implantation with a gate length of 0.8 μm and a gate width of 300 μm.
) The parameters of the equivalent circuit were determined from the actual measured values of a shutt-chip parier diode obtained by shorting the drain and source of a GaAs FET, and the parameters were calculated based on the calculation results.

FIG. 4 is a graph showing the change in the oscillation frequency of the oscillator with respect to the reverse bias direct pressure of the frequency IPI adjusting varactor when the frequency adjusting varactor having the characteristics shown in FIG. 3 is used.

Here, the oscillation FETQs, Q2 has a gate length of 0.8 A m and a gate width of 100 tim (7
) GaAsF E T , inductors Lx and Lz are 0
．． 36 nH, capacitors CI and C2 were set to 0.3 pF. In addition, when (a source follower is used as an amplifier, c)) I) Supply power s, D=
5V, vss=-5V. From the figure, when the reverse bias voltage of the frequency adjustment varactor is in the range of -1 to -2■, that is, from Fig. 3, when the junction capacitance of the frequency adjustment varactor is in the range of 0.33 to 0.23pF, the oscillation frequency is approximately IG.
It can be seen that H2 is changing. Therefore, the modulation sensitivity of the oscillator at this time is approximately IGHz/V.

Next, the computer shimmy results of the relationship between each element value and the oscillation frequency when the capacitor CcP is connected in parallel with the inductors Ls and Lz of FIG. 2 are shown in the graph of FIG. 8g5. In order to simplify the calculation, in the simulation, a varactor for frequency adjustment, a buffer angle, and an FET for the current source are used.
is omitted, and the gate length of the oscillation FET is 0.8 μm,
The gate width is 300 μm, and the load of the oscillator is made of GaAs F E '1' with a resistance of IKΩ. From this figure, when the inductance L=0, 25 nH, the capacitance Cc of the capacitor connected in parallel with the inductor is 0.3 to 0.6 p.
It can be seen that the oscillation frequency changes by about 2 GH within the F range.

If this capacitance is to be realized by a varactor, a reverse bias voltage of approximately -1, 2 to -0, 1 ■ should be applied to the varactor, as shown in Figure @3. Therefore, the modulation sensitivity of the oscillator at this time is approximately 2 GH,/V.

[Problem to be solved by the invention]

When an oscillation frequency (for example, X band or higher) is required for the above-mentioned conventional MMIC voltage controlled voltage controlled oscillator, the element sensitivity of each element to the oscillation frequency increases, and the oscillation to the reverse bias voltage applied to the varactor increases. The rate of change in frequency also increases, ie, the modulation sensitivity of the voltage controlled oscillator increases. This voltage controlled oscillator includes a frequency adjusting varactor D1. In addition to the oscillation frequency control by Dz,
Inductor L1. It can be seen that similar control of the oscillation frequency is possible even if a varactor is inserted in parallel with Lt, but the modulation sensitivity is quite high, on the order of GHZ/V.

When this voltage controlled oscillator is used to configure a phase-locked loose circuit with an external PLL configuration circuit, there is a problem that the phase noise of the system increases, and the oscillation frequency decreases due to the RF acid component noise entering the DC line. Since the probability of fluctuations increasing, a highly stable power source is required for oscillators that require high same-wavenumber stability. Also, D.C.
There are drawbacks such as an increase in pellet size due to frequent use of bypass capacitors on the line, that is, an increase in pellet cost.

One possible solution to these problems is to use a varactor with low voltage sensitivity, but when implementing an MMIC, a GaAs Schittky barrier diode will be used as the varactor, which reduces the voltage sensitivity of its junction capacitance. To do this, it is necessary to deepen the active layer and create a gradient in carrier concentration depending on the depth, which is difficult to control in terms of process, and even if it could be achieved, a special process would be required. This results in an increase in costs.

Further, if a varactor with low voltage sensitivity is used, the range of change in the oscillation frequency becomes narrow, and the versatility of the oscillator is reduced.

The purpose of the present invention is to eliminate such drawbacks and provide an MMIC voltage that can realize a wide band of oscillation frequencies while preventing an increase in the modulation sensitivity of the oscillator without requiring a varactor with a special structure even at frequencies above the X band. There is a voltage control oscillator.

[Means to solve the problem]

The configuration of the present invention uses GaA 5FE as an oscillation active element.
An inductor and a first capacitor (or a second varactor in a reverse bias state) with T as an excavation frequency determining element.
The voltage control system consists of an unstable multivibrator equipped with a buffer amplifier at the output section, using a first varactor put in a reverse bias state by a control voltage applied from the first terminal as an excavation frequency adjustment element, respectively. In the oscillator, a second capacitor is connected in series to the first varactor so as to reduce the range of capacitance change of the first varactor, and a second capacitor is connected to the connection point from the outside via a second terminal and an RF blocking resistor. A voltage is applied that puts the first varactor in a reverse bias state, a third varactor is connected to the front g pin induct via a parallel I DC blocking capacitor, and a third terminal and an RF blocking capacitor are connected to this connection point. It is assumed that a voltage is applied from the outside through the resistor to put the third varactor in a reverse bias state.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram of an embodiment of the present invention. In this embodiment, in order to solve the conventional drawbacks, as shown in FIG. 1, for the purpose of reducing modulation sensitivity, a frequency adjustment varactor D1. These varactors I
Capacitors Cs and Cs are connected in series with h and Dz, respectively, and a varactor reference voltage supply terminal 14.15 and a sufficiently high RF blocking resistor R of resistor ll& are connected at the connection point.
A reference voltage is applied externally via a and Rs to maintain the reverse bias state of the varactors DI and Dz.

Moreover, the narrowing of the frequency range caused by this is caused by the inductor L1. It is in a reverse bias state by a control voltage vcoNTg that is applied from the outside through DC blocking capacitors C3 and C4 in parallel with L2 and through control voltage supply terminals 12.13 and RF blocking resistors Rz and Rs with sufficient resistance. Second varactors Da and D4 are connected. The problem is solved because the oscillation frequency changes as shown in Fig. 8g5 due to the junction capacitance of the varactors depending on the reverse bias voltage value of these varactors Ds and Da.

Here, the second varactor D3. D4 control pressure VCONT
2 shifts the oscillation frequency to a necessary oscillation frequency, for example, near fl, within the oscillation frequency range of the oscillator, and this becomes a fixed voltage.

On the other hand, the control voltage vcoNr□ of the 810 frequency adjustment varactors DI and Dz is connected to the PLL for the purpose of stabilizing the oscillation frequency.
It is applied from an IC or the like, and constantly changes as the oscillation frequency fluctuates.

Next, as a specific example, the frequency adjustment varactor D shown in FIG.
I, D2 is 0.3 for a reverse bias voltage of θ~2v
Assuming that the junction capacitance changes in the range of ~0.6 pF,
When a 0.3 pF capacitor is connected in series with this, the combined capacitance becomes 0.15 to 0.2 pF, and the junction capacitance Suga ill becomes 1/6 for the same reverse bias voltage. At this time, in response to the decrease in the valley value, the inductor L*
, Lz is increased and the oscillation frequency is kept at a constant value, the modulation sensitivity of the oscillator can be expected to be reduced by the same amount as the reduction in the junction capacitance change range.

Note that the control voltage VcoNrz of the second varactors Ds and Da
If it is made variable by using a semi-fixed volume or the like, variations in the 001 path elements can be absorbed.

Further, although fixed capacitors C1 and C2 are used as the oscillation frequency determining capacitors in this embodiment, the same effect can be obtained even if a reverse biased varactor is used instead.

〔Effect of the invention〕

As explained above, the present invention connects a series capacitor to the frequency A wall varactor of an MMIC pressure-controlled oscillator having an unstable multivibrator configuration to narrow the range of change in junction capacitance due to the reverse bias voltage of the varactor. By connecting a second reverse-biased varactor in parallel with the oscillation frequency determining inductor via a DC blocking capacitor, wideband oscillation can be achieved while suppressing the modulation sensitivity of the oscillator even at oscillation frequencies above the X band. It becomes possible.

Therefore, there are the following effects.

1) Cost can be reduced because no special varactor is required.

2) Since the modulation sensitivity is reduced, frequency fluctuations caused by RF acid component noise entering the DC line are reduced, and D
The number of bypass capacitors on the C line can be reduced, the pellet size can be reduced, and when a femelock loop is configured with an external PLL configuration circuit, the phase noise of the system can be reduced.

3) The oscillation frequency band is wide, so it has great versatility.

4) Since the control voltage of the second varactor can be varied manually, variations in element values can be absorbed to some extent.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of an example of an MMIC voltage controlled voltage controlled oscillator according to the present invention, Fig. 2 is a circuit diagram of an example of a conventional MMIC voltage controlled oscillator, and Fig. 3 is the inverse of the varactor shown in Fig. 2. A graph showing the relationship between bias voltage and junction capacitance. Figure 4 is a graph showing the relationship between each element value and excavation frequency of the circuit in Figure 2 as a conventional example, obtained by computer simulation. Figure 5 is a graph showing the relationship between
It is a graph showing the relationship between the capacitance of the capacitor, the inductance of the inductor, and the oscillation frequency of the oscillator when a capacitor is connected in parallel to the oscillation frequency determining inductor shown in the figure. 1.2...Buffer amplifier, 11-15...
...Voltage application terminal, 16.17...Output terminal, 18-20...'Power terminal, Ql, C2...
...GaAs FET for oscillation, Qs...'
Kl! Il! , source FET%n, *Dz +D3 e
D4...Oscillation frequency adjustment backter = demand = ヰ,
Cs, Cz, -0-0 oscillation frequency determining capacitor, C3゜C4...DC blocking capacitor, C5
, C6... Capacitor, Lx, Lx...
・Inductor for determining oscillation frequency, R1 to Rs...
・RF blocking resistor. Rod 1 diagram

Claims (1)

[Claims] A GaAsFET is used as an oscillation active element, an inductor and a first capacitor (or a second varactor in a reverse bias state) are used as an oscillation frequency determining element, and a control voltage applied from the first terminal serves as an oscillation frequency adjusting element. In a voltage controlled oscillator comprising an unstable multivibrator using first varactors placed in a bias state and having a buffer amplifier at an output section, the first
A second capacitor is connected in series to this first varactor so as to reduce the capacitance change range of the varactor, and the first varactor is connected to this connection point from the outside via a second terminal and an RF blocking resistor. Apply a voltage to reverse bias,
A third varactor is connected in parallel to the inductor via a DC blocking capacitor, and this third varactor is externally reverse biased via a third terminal and an RF blocking resistor at this connection point. A voltage controlled oscillator characterized by applying a voltage.