JPH06164256A - High frequency driving circuit for mosfet - Google Patents

Abstract

PURPOSE:To effectively drive a high frequency/large power amplifier circuit which uses one or plural pieces of MOSFET having the large gate input capacity. CONSTITUTION:The gates of a group 7 of plural pieces of MOSFET connected in parallel to each other are driven with high frequency by a high frequency signal source 1 through a driving transformer 3 and a capacitance 5. In this case, fn<f is satisfied between the frequency (f) of the source 1 and the resonance frequency (fn) secured between the parasitic inductance Ls of the route reaching the gate of the group 7 from the transformer 3 and the gate capacity Cg of the group 7. The series resonance frequency f1 defined between the inductance Ls and the series synthetic capacity Cx of the capacity of the capacitance 5 and the capacity Cg is set approximately equal to the frequency (f) and the series resonance is generated. Thus a high frequency driving circuit is efficiently driven.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency drive circuit for MOSFETs, and more particularly to a high frequency drive circuit for MOSFETs for high power amplification.

2. Description of the Related Art Application of high frequency power, industrial, scientific,
In the shortwave band as a medical frequency, 13.560MHz and 2
7.120MHz is specified. MOSFETs are suitable for this type of high frequency power amplification because they have essentially no stored carriers. FIG. 5 (c) is an example of a high frequency power amplifier circuit in which 10 MOSFETs are connected in parallel. In Figure 13.5
From the high frequency signal source 1 of 60MHz, through the drive transformer 3,
A MOSFET group 7 in which 10 MOSFETs are connected in parallel is driven. The drive transformer 3 is for both impedance conversion and insulation, and is a step-down type with a winding ratio of the primary winding to the secondary winding of 5 to 10: 1. This structure has reduced leakage inductance. If this circuit is equivalently rewritten, it becomes FIG. 5 (d). 1'is a signal source converted to the secondary side of the drive transformer 3, Ls is the total inductance including parasitic inductance including the leakage inductance of the drive transformer 3 and the inductance of the wiring, and Rg is the gate equivalent resistance of the MOSFET group 7. It is normally several ohms, and here it is 1 ohm. Cg is a combined gate capacitance of the MOSFET group 7. In this circuit, industrial frequency 13.560MHz
When 10 MOSFETs with a gate capacitance of 800 pF are connected in parallel at, the total gate input capacitance Cg is 8000 pF.
Is. 13.5 in combination with this total gate input capacitance Cg8000pF
The inductance value Ls that resonates at 60MHz is calculated as Ls = 17.2nH from the resonance frequency formula. Such a minimum inductance is difficult to achieve even with a careful layout, and usually exceeds this value. As a result, the resonance frequency fn between the parasitic inductance Ls and the total gate input capacitance Cg becomes lower than the drive frequency f of the high frequency source 1, and the MOSFET group 7 cannot be efficiently driven.

SUMMARY OF THE INVENTION The present invention is directed to a single MOSFET or a plurality of MOSFETs having such a large gate input capacitance.
It is an object of the present invention to obtain a high frequency drive circuit capable of efficiently driving a.

In order to solve this problem, in the present invention, as a first means, a high frequency signal source is used to drive a high frequency from a high frequency signal source to a gate of a single MOSFET or a plurality of MOSFETs connected in parallel having a gate capacitance Cg. A circuit, characterized by having the following conditions:
A high frequency drive circuit of OSFET is proposed. Parasitic inductance Ls of the path from the drive transformer to the MOSFET gate and MOSFET gate capacitance Cg
And the resonance frequency fn is fn with respect to the frequency f of the high frequency signal source.
<F. Capacitance in series between high frequency source and gate
Connecting Cs. This capacitance Cs and MOSFET gate capacitance Cg
The series resonance frequency f1 of the series combined capacitance Cx and the parasitic inductance Ls of is equal to the frequency f of the high frequency signal source. Secondly, the following means are proposed. A high frequency signal source 1; a drive transformer 3 connected to the high frequency source 1 to a primary winding 3a; a capacitance 5 connected to one end of a secondary winding 3b of the drive transformer 3; a single or a plurality of First MOSFET formed by connecting MOSFETs in parallel
A group 13; a second MOSFET group 15 in which a single MOSFET or a plurality of MOSFETs are connected in parallel; and these first MOSFs
A common conductor 27 that connects the source of the ET group 13 and the source of the second MOSFET group 15 in common; and a current balancer 23 having windings 23a and 23b.
One end of the winding 23a is connected to the gate of, and the other end of the winding 23a is connected to one end of the secondary winding 3b of the drive transformer 3,
One end of the winding 23b is connected to the gate of the second MOSFET group 15, and the other end of the winding 23b is composed of a current balancer 23 connected to the other end of the capacitance 5
A high frequency drive circuit of ET, which includes a parasitic inductance Ls of a path from the drive transformer 3 to the gates of the first and second MOSFET groups 13 and 15, and first and second MOSFs.
The resonance frequency fn with the gate capacitance Cg of the ET groups 13 and 15 is fn <f with respect to the frequency f of the high frequency signal source 1, and the capacitance Cs of the capacitance 5 and the first and second MOSFET groups 13 and 1
5. A high frequency drive circuit for a MOSFET, wherein the series resonance frequency f1 of the series combined capacitance Cx of the total gate capacitance Cg of 5 and the parasitic inductance Ls is substantially equal to the drive frequency f.
Thirdly, the following means are proposed. A high frequency signal source 1; a drive transformer 3 in which the high frequency source 1 is connected to a primary winding 3a; and a secondary winding 3b of the drive transformer 3.
A capacitance 5 connected to one end of; a first MOSFE formed by connecting a single MOSFET or a plurality of MOSFETs in parallel
T group 13; second MOSFET group 15 in which a single MOSFET or a plurality of MOSFETs are connected in parallel; these first MOSs
A first current balancer 23 having a common conductor 27 for commonly connecting the source of the FET group 13 and the source of the second MOSFET group 15; windings 23a and 23b,
One end of the winding wire 23a is connected to the gate of the ET group 13, one end of the winding wire 23b is connected to the gate of the second MOSFET group 15, and the other end of the winding wire 23b is connected to the other end of the capacitance 5. A first current balancer 23; and a single or multiple M's
Third MOSFET group 17 in which OSFETs are connected in parallel 17
And a fourth MOSFET group 19 in which a single MOSFET or a plurality of MOSFETs are connected in parallel; and these third MOSFETs
A second current balancer 25 having a common conductor 29 for commonly connecting the source of the group 17 and the source of the fourth MOSFET group 19; windings 25a and 25b,
One end of the winding 25a is connected to the gate of 17 and the fourth MOS
A second current balancer 25 in which one end of a winding 25b is connected to the gate of the FET group 19 and the other end of the winding 25b is connected to the other end of the capacitance 5; and a third current balancer 25 having windings 21a and 21b. Current balancer 21 of which the other end of the winding 23a of the first balancer 23 is connected to one end of the winding 21a
The other end of the winding 23a of the second balancer 25 is connected to one end of 21b, and the other end of the winding 21a and the other end of the winding 21b are connected to one end of the secondary winding 3b of the drive transformer 3. A high-frequency drive circuit for a MOSFET composed of a current balancer 21 and a drive transformer 3 from the first to fourth MO
The parasitic inductance Ls of the path to the gates of the SFET groups 13, 15, 17, 19 and the first to fourth MOSFET groups 13, 15,
The resonance frequency fn with the gate capacitance Cg of 17,19 is fn <f with respect to the frequency f of the high-frequency signal source 1, and the capacitance Cs of the capacitance 5 and the first to fourth MOSFET groups 13, 15, 17, 1
9. A high frequency drive circuit for a MOSFET, wherein the series resonance frequency f1 of the series combined capacitance Cx of the total gate capacitance Cg of 9 and the parasitic inductance Ls is substantially equal to the drive frequency f.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 (a) shows an embodiment of a high frequency drive circuit for a MOSFET according to the present invention, and FIG. 1 (b) shows its equivalent circuit. In FIG. 1 (a), a high-frequency signal source 1 with a frequency of 13.560 MHz drives a gate of a MOSFET group 7 in which 10 MOSFETs are connected in parallel with each other through a drive transformer 3 and a capacitor 5 connected in series. To do.
As shown in the equivalent circuit in Fig. 1 (b), the circuit in Fig. 1 (a) has gate capacitances Cg and Cs in series, so the combined capacitance Cx is Cx.
= Cg x Cs / (Cg + Cs), which is smaller than either Cg or Cs. Therefore, the parasitic inductance Ls can be made to resonate at the frequency f of the high frequency source 1 by selecting an appropriate value for Cs. For example, the parasitic inductance Ls
In the case of 100nH, the capacitance that resonates at 13.560MHz is calculated.
It will be 1380pF. Then, when the gate capacitance Cg = 8000pF is combined in series to calculate Cs for 1380pF, Cs = 1670pF.
When the gate equivalent resistance Rg is 1 ohm and the equivalent signal voltage is 5V, the reactance of Ls, Cs, Cg, etc. becomes 0 due to series resonance, and the total voltage of 5V across the gate equivalent resistance Rg.
Occurs. Therefore, the current at this time is 5V / 1Ω
= 5A. The voltage across the gate capacitance Cg is 7.3V when this current value is multiplied by the reactance of Cg. The gate-source voltage Vgs is obtained by calculating the square root of the root mean square value of the voltage 5V of the gate equivalent resistance Rg and the voltage 7.3V across the gate capacitance Cg. The value is Vgs = 8.8V, and it can be driven sufficiently. FIG. 2 is a resonance characteristic diagram for explaining the operation of this circuit. In the figure, the broken line shows the conventional resonance characteristic, and the solid line shows the resonance characteristic of the circuit of the present invention shown in FIG. According to the present invention, by adding the capacitor 5, the resonance frequency of the gate drive circuit is changed from fn to
It rises to f1 and becomes almost equal to the frequency f of the high frequency source 1, and the gate voltage Vgs becomes almost the maximum value. Therefore, the MOSFET can be efficiently driven. FIG. 3 shows an example in which the present invention is applied to parallel driving of MOSFETs operating in a push-pull circuit. In the figure, 1 is frequency 13.5
It is a high-frequency signal source of 60MHz, 3 is a drive transformer with a winding ratio of 8: 1, and 5 is a capacitor. Also, 7 and 8 are MOSF in which 10 MOSFETs are connected in parallel.
It is an ET group. When the gate-source of the MOSFET group 7 is forward-biased and turned on, the gate-source of the MOSFET group 8 is reverse-biased and turned off, and the push-pull operation is performed. At this time, the capacitor 5 resonates in series with the frequency of the high-frequency signal source 1 as described in FIG. 1, and efficiently drives the MOSFET groups 7 and 8. FIG. 4 is an example in which the present invention is applied to parallel driving of MOSFETs operating in a push-pull circuit and further a current balancer is used. In the figure, 1 is frequency 13.5
It is a high-frequency signal source of 60MHz, 3 is a drive transformer with a winding ratio of 8: 1, and 5 is a capacitor. Also 13, 15,
Reference numerals 17 and 19 denote MOSFET groups in which five MOSFETs are connected in parallel. Reference numerals 21, 23, and 25 are current balancers, respectively, which have a structure in which two conductors penetrate through the holes of the ring core with the polarities shown in the figure, and equivalently constitute a transformer with one turn each. . In the current balancer 21, the value i1 of the current flowing through one winding 21a is
When the value of the current i4 flowing through b is larger than the value of the current i4, the large amount of the current causes the winding 21a to act as an inductance and gradually reduce the current i1. The other current balancers 23 and 25 operate similarly. Explaining the configuration, the high frequency signal source 1
Is connected to the primary side of the drive transformer 3 having a winding ratio of 8: 1. One end of the secondary winding of the drive transformer 3 is connected to one end of the winding 21a of the current balancer 21, and the other end of the winding 21a is connected to the gate of the MOSFET group 13 via the winding 23a of the current balancer 23. It The source of the MOSFET group 13 is a MOS
The source of the FET group 15 and the common conductor 27 are connected. This common conductor has a large area and is located at the ground potential in terms of high frequency. Another common conductor 29 is commonly connected to this common conductor 27. Next, the gate of the MOSFET group 15 is connected to one end of the capacitor 5 via the winding wire 23b of the current balancer 23. The other end of the capacitor 5 is connected to the other end of the secondary winding of the drive transformer 3. Similarly, one end of the secondary winding of the drive transformer 3 is connected to the winding 21 of the current balancer 21.
It is connected to one end of b and the other end of winding 21b is a current balancer 25.
Is connected to the gate of the MOSFET group 17 via the winding 25a. The source of the MOSFET group 17 is connected to the source of the MOSFET group 19 and the common conductor 29. Next MOSFET
The gate of group 19 is connected to one end of capacitor 5 via winding 25b of current balancer 25. The other end of the capacitor 5 is connected to the other end of the secondary winding of the drive transformer 3. In this way, the MOSFET groups 13 and 15 are connected in series with opposite polarities. Similarly, the MOSFET groups 17 and 19 are connected in series with opposite polarities. In the high-frequency drive circuit of the MOSFET thus configured, the current balancers 21, 23, 25 operate so that the current values of the MOSFET groups 13, 15, 17, 19 become equal to each other. In addition, the capacitor 5 is inserted and connected in series with the secondary winding of the drive transformer 3,
Combined with the total capacitance of the ET groups 13, 15, 17, and 19, each MOSFET can be efficiently resonated in series with stray inductance.
Drive the gate of. Furthermore, since the number of turns of the secondary winding 3b of the drive transformer 3 is one, it is not possible to accurately capture the midpoint. However, in this embodiment, each MOSFET group 13, 1 viewed from the secondary winding 3b of the drive transformer 3 is
The gate circuits of 5, 17, 19 are symmetrically configured,
And each M in which the common conductors 27 and 29 are push-pull connected
Since it is connected to the sources of the OSFET groups 13, 15, 17, and 19, it operates in a balanced manner without grounding the neutral point. In this circuit, even if the number of MOSFETs increases, the balanced operation is guaranteed in combination with the action of the current balancer. In this embodiment, the MOSFET groups 13, 15, 17, 19 are
The present invention is not limited to the group consisting of a plurality of MOSFETs, but can be similarly applied to a single MOSFET having a large current capacity. Regarding the number of turns of each winding of the current balancers 21, 23 and 25, one turn is a preferable example, but the number of turns is not necessarily one turn, and an optimum value can be selected according to usage conditions. Further, in the embodiment shown in FIG. 4, a circuit in which the MOSFETs 17 and 19 and the current balancers 21 and 25 are omitted may be used.

Since the present invention has the characteristics as described above, even if the number of MOSFETs connected in parallel increases and the gate capacitance increases, the series resonance with the parasitic inductance of the gate circuit can be used to achieve efficient Can be driven to. Further, in the case of the push-pull circuit, when the current balancer is also used, the difference in each current value due to the difference in mutual distance of many MOSFETs is more perfectly balanced. On the other hand, the inductance component due to the current balancer can be canceled by the capacitance inserted in the drive circuit to cause series resonance, and the MOSFET group can be efficiently driven. In this way, even if the number of MOSFETs increases, the balance operation is ensured in combination with the action of the balancer. Therefore, the efficiency of the high frequency high power amplifier can be improved.

[Brief description of drawings]

FIG. 1 shows an embodiment of a high frequency drive circuit for a MOSFET according to the present invention.

FIG. 2 is a resonance characteristic diagram for explaining the operation of the circuit shown in FIG.

FIG. 3 shows a circuit in which a high-frequency drive circuit for a MOSFET according to the present invention is implemented as a push-pull circuit.

FIG. 4 shows a circuit in which a high-frequency drive circuit for a MOSFET according to the present invention is implemented as a push-pull circuit and further uses a current balancer.

FIG. 5 shows an example of a conventional high frequency drive circuit for a MOSFET.

[Explanation of symbols]

1 ... High frequency signal source 3 ... Driving transformer 5 ... Capacitors 7, 8, 13, 15, 17, 19 ... MOSFET group 21, 23, 25 ... Current balancer 27, 29 ... Common conductor

Claims (3)

[Claims] 1. A single or a plurality of parallel-connected MOs having a gate capacitance Cg from a high frequency signal source through a drive transformer.
A circuit for driving a gate of an SFET at a high frequency, wherein a resonance frequency fn between a parasitic inductance Ls of a path from the high frequency signal source to the gate of the MOSFET and a gate capacitance Cg of the MOSFET becomes a frequency f of the high frequency signal source. On the other hand, fn <f, and a capacitance Cs is connected in series between the high frequency signal source and the gate, and this capacitance Cs and the gate capacitance Cg of the MOSFET are
A high frequency drive circuit for a MOSFET, wherein the series resonance frequency f1 of the series combined capacitance Cx and the parasitic inductance Ls is substantially equal to the frequency f of the high frequency signal source. 2. A high-frequency signal source 1, a drive transformer 3 having the high-frequency source 1 connected to a primary winding 3a, and a capacitance 5 connected to one end of a secondary winding 3b of the drive transformer 3.
A first MOSFET group 13 in which a single MOSFET or a plurality of MOSFETs are connected in parallel; and a single or a plurality of MOSFs
A second MOSFET group 15 formed by connecting ETs in parallel; a source of the first MOSFET group 13 and a second MOSF
A common conductor 27 that connects the sources of the ET group 15 in common; and a current balancer 23 having windings 23a and 23b,
One end of the winding 23a is connected to the gate of the MOSFET group 13 of the other, and the other end of the winding 23a is connected to the secondary winding 3b of the drive transformer 3.
A current balancer 23 connected to one end of the second MOSFET group 15, one end of a winding 23b connected to the gate of the second MOSFET group 15, and the other end of the winding 23b connected to the other end of the capacitance 5. Of a high-frequency signal source 1 to a first to a second MOSFET group 1
The parasitic inductance Ls of the path to the gate of 3,15,
The resonance frequency fn with the gate capacitance Cg of the first and second MOSFET groups 13 and 15 is fn with respect to the frequency f of the high frequency signal source 1.
<F, the capacitance Cs of the capacitance 5 and the first or second MOSF
A MOSF characterized in that the series resonance frequency f1 of the series combined capacitance Cx of the total gate capacitance Cg of the ET groups 13 and 15 and the parasitic inductance Ls is substantially equal to the frequency f of the high frequency signal source 1.
High frequency drive circuit of ET. 3. A high frequency signal source 1, a drive transformer 3 having the high frequency source 1 connected to a primary winding 3a, and a capacitance 5 connected to one end of a secondary winding 3b of the drive transformer 3.
A first MOSFET group 13 in which a single MOSFET or a plurality of MOSFETs are connected in parallel; and a single or a plurality of MOSFs
A second MOSFET group 15 formed by connecting ETs in parallel; a source of the first MOSFET group 13 and a second MOSF
A first current balancer 23 having a common conductor 27 commonly connecting the source of the ET group 15 and windings 23a and 23b, wherein one end of the winding 23a is connected to the gate of the first MOSFET group 13. , Winding 23 on the gate of the second MOSFET group 15
a first current balancer 23 having one end of b connected to the other end of the winding 23b connected to the other end of the capacitance 5; and a third MOSFET group 17 in which a single MOSFET or a plurality of MOSFETs are connected in parallel. And a fourth MOSFET group 19 in which a single MOSFET or a plurality of MOSFETs are connected in parallel; a source of the third MOSFET group 17 and a fourth MOSFET group
A common conductor 29 commonly connected to the sources of 19; winding 25a
A second current balancer 25 having
One end of the winding 25a is connected to the gate of the MOSFET group 17, and one end of the winding 25b is connected to the gate of the fourth MOSFET group 19, and the other end of the winding 25b is connected to the other end of the capacitance 5. Second current balancer 25; winding 21a
21b is a third current balancer 21 having one end of its winding 21a connected to the other end of the winding 23a of the first balancer 23 and one end of its winding 21b of the second balancer 25. Winding
The other end of 23a is connected to the other end of winding 21a
A high frequency drive circuit of a MOSFET including the current balancer 21 connected to one end of the secondary winding 3b of the drive transformer 3 at the other end of 21b. The high frequency signal source 1 to the first to fourth MOSFETs.
The resonance frequency fn between the parasitic inductance Ls of the path to the gates of the groups 13,15,17,19 and the gate capacitance Cg of the first to fourth MOSFET groups 13,15,17,19 is the frequency of the high frequency signal source 1. fn <f with respect to f, the capacitance Cs of the capacitance 5 and the first to fourth MOSFs
Series gate capacitance of total gate capacitance Cg of ET group 13,15,17,19
The series resonance frequency f1 of Cx and the parasitic inductance Ls is substantially equal to the frequency f of the high frequency signal source 1, M
High frequency drive circuit of OSFET.