JPS59181827A - High frequency switching circuit - Google Patents

Abstract

PURPOSE:To operate the circuit at a board frequency band without requiring circuit space by coupling densely the primary circuit of which a transmission/ receiving coil is connected and the secondary circuit to which a control current is applied by means of a transformer. CONSTITUTION:When the control current Ic reachs 0 at the secondary circuit at the transmission mode, the primary coil L1 acts like a high frequency choke with high impedance, and when a high frequency power output from a transmitter is applied to a high frequency input terminal 12, only the path of an input/ output terminal 14 for transmission/receiving coil is turned on. When the control current Ic is a positive current I0 at the secondary circuit in the receiving mode, the impedance of the primary coil L1 is made very low in terms of high frequency and only the path of the input/output terminal 14 and a detecting signal output terminal 15 is turned on. Thus, no circuit space is required and the circuit is operated at a wide frequency. Then, the high frequency switching circuit with less loss is realized by a simple circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a high frequency switching circuit that is necessary when transmitting and receiving high frequency waves using a single coil in a pulsed NMR device or the like.

Nuclear magnetic resonance (NMR) is a method of obtaining chemical information using the magnetic properties of atomic nuclei. In other words, when an atomic nucleus in a static magnetic field is excited with high-frequency energy, the density of the atom and its bonding state with 1 can be determined from the resonance signal (hereinafter referred to as NMR signal) generated by the resonance phenomenon. The N1.iR device using this principle has recently attracted attention as a diagnostic device that provides anatomical and functional information.

When transmitting and receiving high frequency waves using a single coil in a pulse NMR apparatus or the like, a high frequency switching circuit 1 as shown in FIG. 1 is required. That is, in the transmission mode, the high frequency switching circuit 1 is connected to the high frequency connecting circuit 2.
The transmitting/receiving coil 3 is turned on (the state shown in the figure), and the transmitting/receiving coil 5 generates a pulse-like transmitting output as shown in FIGS. 2(A) and 2(K). When the receiving mode is entered after the transmission output is generated, the high frequency switching circuit 1 is switched to connect the transmitting/receiving coil 6 with the high frequency receiving circuit 4, as shown in FIG.
) is applied to the high frequency receiving circuit 4.

As a conventional example of the high frequency switching circuit as mentioned above, 4
Fig. 3 shows an example using a 1/4 wavelength (λ/4) line. In a circuit with such a configuration, when the high frequency power output from the transmitter is applied to the input terminal 5, the diode D1.
D2. D3. D4 is turned on. Therefore, due to the properties of the quarter-wavelength line, the impedance when looking from point A toward the output terminal B is infinite, and the impedance when looking from point A to the coil 3 is finite. As a result, if matching is achieved, most of the transmission power from the transmitter is applied to the transmitter/receiver coil 3. In the reception mode, the detection output from the coil 3 to the transmitter/receiver 4 is a minute signal, so it is smaller than the forward voltage of the diode,
is off. As a result, the detection output from the transmitting/receiving coil 3 is sent to the receiving circuit via the output terminal 6.

In the case of the above-mentioned circuit, there is a drawback that as the frequency becomes lower, the quarter wavelength (λ/4) line becomes longer and a larger circuit space is required. Another drawback is that it operates normally only at a single frequency and malfunctions when the frequency changes.

In addition, there are various types of high frequency switching circuits, but they are required to have low high frequency transmission power and low loss of induced voltage.

The present invention has been devised to solve the above-mentioned problems, and an object of the present invention is to realize a high-frequency switching circuit that does not require circuit space, operates in a wide frequency band, and has low loss.

According to the present invention, the primary side circuit to which the transmitting/receiving coil is connected and the secondary side circuit to which the control current is applied are closely coupled by a transformer, and two diodes are connected in relation to both ends of the secondary coil, Turn on and off this diode with a control current to
If the next coil is opened for a short period at high frequency, K will be 1
In addition to turning on or off the next circuit, the secondary coil is insulated from the common by a high frequency choke, and the induced current prevention means is used to prevent the secondary coil from being induced by the control current. W
The above object can be achieved by preventing current from occurring in the primary coil.

The present invention will be explained below based on the drawings.

FIG. 4 is a circuit configuration diagram showing an embodiment of the high frequency switching circuit according to the present invention. High frequency switching circuit 1
1, 12 is a high frequency input terminal to which the high frequency transmission output from the transmitter is applied; Di and D2 are diodes each having one end connected to this high frequency input terminal 12 and connected in antiparallel to each other; 14 is this antiparallel connection. The input/output terminal for the transmitting/receiving coil connected to the other end of the diode Di and D2, 16 is a main part of the high frequency switching circuit, and T1 has one end of the primary coil L1 connected to the anti-parallel diode Di.
, a tightly coupled transformer connected to the other end of D2, D3. D
An antiparallel connected diode 15 to which the other end of the primary coil L1 of the four-point transformer T1 is connected to one end and the other end is connected to a common, and 15 is connected to the one end of the antiparallel diode to receive a detection signal. 13 is a control input terminal to which a control current is applied; L5 is an inductance or high-frequency choke λD5.L5 whose one end is connected to the control input terminal 13; D6 is a diode 1L3.D6 whose one end (here, the anode side) is connected to the other end of the high frequency choke L5. L4 has one end connected to this diode D5. Inductances or high frequency chokes, C1 and C2, each connected to the other end (cathode side in this case) of D6 and the other end connected to a common, have one end connected to the diode D5. These capacitors are connected to the other ends of the transformer T1, and the other ends thereof are connected to both ends of the secondary coil L2 of the transformer T1 to form induced current prevention means, and have low impedance with respect to high frequencies.

The operation of the circuit configured as above will be explained below. Connect the control current to the secondary circuit in transmission mode.

becomes 0, the diode D5. D6 is turned off.

At this time, when the high frequency power output from the transmitter is applied to the high frequency input terminal 12 in the primary circuit, the diode D1. D2 is turned on. On the other hand, in the secondary circuit including the secondary coil L2 of the transformer T1, the high frequency choke L
3. Since L4 exhibits high impedance at high frequencies, 2
Both ends of the next coil L2 are in an open state in terms of high frequency,
The primary coil L1 acts as a high impedance high frequency choke. As a result, in the primary circuit, the path between the high frequency input terminal 12 and the detection signal output terminal 15 is off, the path between the high frequency input terminal 12 and the transmitting/receiving coil input/output terminal 14 is not on, and the transmitting circuit Almost all of the high frequency power output from the is supplied to the transmitting and receiving coils. When the control current becomes negative (positive current) in reception mode, the current becomes high frequency TEYO C0.
The diode D5 is turned on through the path of ○-ri L5 → high frequency choke L3 → common, and the diode D6 is turned on through the path of high frequency choke L5 → high frequency choke L4 → common. As a result, both ends of the secondary coil L2 of the transformer T1 become short-circuited at high frequencies via the capacitors C1 and C2, and the impedance of the primary coil L1 can be reduced to an extremely low value at high frequencies. When a minute detection signal from the transmitting/receiving coil is applied to the input/output terminal 14, the path to the high frequency input terminal 12 is processed by the diodes Di and D3, and the signal is received via the path to the detection signal output terminal 15 which is in the on state. Output to the circuit. At this time, the diode I connected in antiparallel
)3. D4 is turned off in response to a small detection signal. In this way, the on/off of the high frequency switching circuit in Figure 4 is as follows:
It can be controlled by turning the control current on and off.

In this case, since the control current does not flow through the secondary coil L2, the ON/OFF rC of the control current causes the transformer T1 to turn 1.
No induced current is generated in the next coil L1 and causes an error in the detection signal. In addition, the entire secondary circuit is equipped with a high frequency choke L.
3. L4. Since it is floating in high frequency from the common by L5, the detection signal output from the detection signal output terminal 15 becomes small due to the stray capacitance between the primary coil L1 of the transformer T1 and the closely coupled secondary coil L2. Not at all.

Note that the diode D5. A negative control current generator can also be used by reversing the polarity of D6.

1, diode D5. D6 and high frequency choke L
3. If a capacitor with uniform characteristics is used as L4, no control current will flow through the secondary coil L2, so the capacitor C1
, C2 can be omitted.

FIG. 5 shows a main circuit of a second embodiment of the present invention, which includes two secondary coils L12. A transformer having Li2, L5 is a high frequency choke whose one end is connected to one end of the secondary coil L13, and D9 is one end (anode terminal here).
is a diode connected to the other end of this secondary coil L13,
Dlo is a diode, D7. D8
One end (here, the anode terminal) is connected to the diode D9. a diode L14 connected to the other end of DIO and whose other ends are respectively connected to both ends of the secondary coil L12;
is a high frequency choke whose one end is connected to the other end of the diode D8 and the other end is connected to common.

The operation of the high frequency switching circuit configured as described above will be described next. In the transmission mode, when the control current is 00 in the secondary circuit, the diodes D7 to DIQ are off and the 92nd coil L12. Since both ends of Li2 are open, the primary coil Lll of the primary side circuit operates as a high frequency choke, as in the case of FIG. Control current engineer in receiving mode. Gaku. (positive current), diodes D7 to DiO are turned on, and secondary coils L12. Both ends of Li2 are short-circuited, and the primary coil Lll has an extremely low impedance at high frequencies, as in the case of FIG. 2
The same control current is passed through the secondary coil L12°Li2, and the magnetic fluxes generated by the secondary coil L12°Li2 are connected in such a way that they cancel each other out.As in the case of FIG. It has the advantage that no current is induced. That is, two secondary coils L12.
The induced current prevention means is formed by using Li2. In addition, the entire secondary circuit is a high frequency Temeek L14.
Since it is floated from the common in terms of high frequency by L5, there is no adverse effect due to stray capacitance between the primary coil and the secondary coil of the transformer T2, which is the same as in the case of FIG. 4.

As described above, according to the present invention, a high frequency switching circuit that does not require circuit space, operates in a wide frequency band, and has low loss can be realized with a simple configuration.

[Brief explanation of the drawing]

1 and 2 are principle explanatory diagrams showing the principle of high frequency switching, FIG. 3 is a circuit configuration diagram showing a conventional example of a high frequency switching circuit, and FIG. 4 is a circuit configuration showing the first embodiment of the present invention. 5 are principal part circuit diagrams showing a second embodiment of the present invention. 1.11...High frequency switching circuit, Engineering...Control current, TI, T2...Transformer, L2. L12. L
L3... Secondary coil, D5-D10... Diode, L3-L5. LL4...High frequency choke, LL,
Lll...Primary coil, CL, C2...Capacitor.

Claims (3)

[Claims] (1) A transformer tightly coupling a primary coil and a secondary coil, one end of which is connected to both terminals of the secondary coil of this transformer, and the other ends are connected to each other, and the control current is connected to the transformer. two diodes that short-circuit or open the secondary coil at least at high frequencies;
A high-frequency switching circuit comprising: a high-frequency choke that increases high-frequency impedance from a common of a secondary coil; and induced current prevention means that prevents induced current caused by the control current from occurring in the primary coil. (2) The high frequency switching circuit according to claim 1, wherein a capacitor is connected between the secondary coil terminal and the diode as an induced current prevention means. (3) As an induced current prevention means, a second secondary coil is provided in the transformer, which generates a magnetic flux by the control current that cancels the magnetic flux generated in the secondary coil of the transformer by the control current. High frequency switching circuit in item 1.