JPS6010907A - Phase shift circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a phase shift circuit used in a vA magnetic field control device in a nuclear magnetic resonance apparatus.

The magnetic field used for nuclear magnetic resonance is required to have a stability of about 10-8 to 10 over a long period of time. To this end, magnetic field control devices have been used that detect magnetic field fluctuations based on magnetic resonance signals and cancel them. This l
A magnetic field control device mixes a control sample into a measurement sample, or places a control sample near the measurement sample, and controls the resonance signals (dispersion) obtained from these control samples in a magnetic field. The magnetic field is stabilized by using it as a control signal and providing negative feedback to the magnet's excitation current control means.

In particular, magnetic field control devices that have been used recently employ a so-called time-sharing method in which a control sample is intermittently irradiated with high frequency waves at a constant cycle, and resonance signals are detected during non-irradiation periods.

By the way, this magnetic field control device uses a high frequency phase shift circuit to ensure the stability of the magnetic field and always satisfy the resonance condition f[/j. FIG. 1 is a circuit diagram showing this phase shift circuit, in which 1 is an input circuit section receiving high-frequency human power Vin, 2 is a first shift circuit section connected to the input circuit 1 via a capacitor C+, 3 Is it capacitor C? The second shift circuit section 2 is connected to the first shift circuit section 2 via
The shift circuit section 4 is a third shift circuit section connected to the second shift circuit section 3 via a capacitor C3.

These shift circuit units 2 to 4 have the same circuit configuration. That is, each of the shift circuit sections 2.3.4 has an LCR parallel resonant circuit connected to its drain and source, and receives an input signal to each shift circuit section 2.3.4 at its gate.
TQ21. Qs 1. Q41, and the FETQ21.
The signal at the drain of Qs 1 and Q41 is connected to the capacitor C2.
r, Cs t and C41, the source signal is given to FETQ22, Qs2, and Q42, and both signals passing through these are added and output to the next stage. The phase shift amount of each shift circuit section 2.3.4 is:
Each FETQzz, Q32. It is determined by the phase control voltage Vc applied to the gate of Q4z. An output circuit section 5 receives the output of the third shift circuit section 4 via a capacitor C4, and outputs an output signal VOut as a phase shift circuit. In addition, the power supply m pressure E is the filter 6@
The signal is applied to each shift circuit section 2, 3.4 and the output circuit 5 via.

By the way, in the conventional circuit with such a configuration, each shift [~
Since it is necessary to increase the Q of the circuit sections 2 and 3.4, even a slight change in the frequency of the input Vin causes problems such as a significant change in the level of the output Volt, a change in the phase variable width, and problems with the phase change. When trying to keep the output level constant when changing it, there was a problem that it would oscillate or overturn. or,
Since there are a large number of parts, there are also problems in that the space taken up on the printed board is large and the cost is also high.

The present invention was developed in view of these problems, and its purpose is to create a phase shifter that can reduce fluctuations in output level with respect to phase shift, does not cause the problem of oscillation, and has a small number of parts. (-To provide a circuit.

The configuration of the present invention that achieves this object is by connecting a plurality of resonant circuits including variable capacitance diodes in series and whose resonance frequencies are shifted from each other, and by changing the control voltage applied to the variable capacitance diodes. , is characterized in that it is configured to change the amount of phase shift.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 2 is a circuit diagram showing an embodiment of the present invention, and in the figure, Fl
is a first resonant circuit whose one end is grounded and which receives the input Vin applied to the other end of the sensor C1o via a capacitor CI+, and F2 is a first resonant circuit which receives the output of the first resonant circuit F1 via a capacitor C12. Resonant circuit No. 2, 1:3 is a third resonant circuit that receives the output of the second resonant circuit F2 via a capacitor C13. Each resonant circuit F1. F2.
F3 are capacitors Co t and Co 2 respectively
,C.

3 and variable capacitance diode D1. D2, a series circuit of DB and a coil Lt connected in parallel to the series circuit.

F2. It is composed of a [C parallel resonant circuit consisting of F3. The gain and phase characteristics of the LC parallel resonant circuit can be shown in FIG. From this figure, it can be seen that this circuit outputs an input signal with a frequency shifted from the resonance frequency f with a phase shift. However, since the function as a bandpass filter is shifted to the right, the gain will also change significantly if it deviates from the resonance frequency f. The above resonant circuit F1. F2. The individual characteristics of F3 are exactly the same as in the case of FIG. 3, but these resonant circuits F+, F
2. Co-Ji frequency vlf I of F3, f2. C3 is
are configured slightly differently (e.g. f, <C2
<C3) and is configured to increase or decrease in response to changes in the control voltage Vc applied to the variable capacitance diodes D+, D2, and DB via the resistors R+, R2, and R3. FIG. 4(a) shows these resonant circuits F1. F2. Figure 4 shows the relationship between the individual gain and phase characteristics of F3, and the gain and phase characteristics of the entire cascade-connected resonant circuit F+, F2, and F3 obtained by combining these characteristics is shown in Figure 4. (b). In this overall characteristic diagram, approximately f1
The gain is approximately flat in the frequency band of ~f3.

Furthermore, the phase variable width increases as the number of resonant circuits increases, and the linearity of phase change also improves.

The output of the final stage resonant circuit F3 is the capacitor C14.
is applied to the capacitor Cts via the capacitor Cts.
15 terminal voltages are configured to input to amplifier A;
The output of the amplifier A is outputted as the output signal vout of the phase shift circuit via the capacitor C20. Incidentally, the capacitor C16°C10 and the coil L4 constitute a filter, and the power supply voltage E is applied to the amplifier A through the filter. Further, Cso is a capacitor connected between the control voltage Vc line and the ground.

According to such a configuration, the variable traffic diodes D1 to D
By changing the control voltage Vc applied to 3, the characteristic curve shown in FIG. 4<b> can be shifted to the lower frequency side or the higher frequency side. Therefore, if the frequency [0 of the input Vin is f2, then by changing the control voltage Vc and moving the characteristic curve to the left by about f3-f2 in FIG. 3(b), , without loss of gain.
The phase of the output Vout can be delayed to φ■.

On the other hand, f2. −f , by moving the degree toward
The phase of the output V out can be changed to φ2 without reducing the gain.
You can proceed up to. That is, by moving the characteristic curve in the range of 11 to f3, the phase of the output vout can be changed to -
It can be varied within the range of φ1 to +φ2, and the output yout can be kept substantially constant within that range. In addition, in the case of this phase shift circuit, the band where the gain is flat can be widened by increasing the number of resonant circuits (three in the above example), so it can sufficiently cope with fluctuations in the frequency 10 of the input Vin. .

Furthermore, by widening the band in this way, the delay time at the phase difference 06 can be reduced, and the good RF pulse (Gat
It is possible to prevent the rise and fall characteristics from being impaired even when inputting RF Pulse (ED RF Pulse). Furthermore, as is clear from the comparison between FIG. 1 and FIG. 2, the circuit configuration is simpler than that of the conventional one, so that a low-cost phase shift circuit can be obtained with the converter 1-. Of course, the problem of oscillation unlike the conventional circuit does not occur.

The configuration of the amplifier Δ portion in the above embodiment is based on the insertion loss (l n5er −5io
nLoss) or ripple is small, it is not necessary. Furthermore, it goes without saying that the number of resonant circuits can be arbitrarily selected, and other configurations can also be selected. for example,
An IC series resonant circuit may be used instead of the LC parallel resonant circuit. Figure 5 shows a C series resonant co-circuit F4 used instead of the LC parallel resonant circuit 1:2 in Figure 2, its resonant frequency chosen in the same way as in the previous case, and a similar phase shift. You can get a@.

As described above, according to the present invention, it is possible to realize a phase shift circuit that can reduce fluctuations in output level compared to phase shift circuits, does not cause the problem of oscillation, and has a small number of parts.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional phase shift circuit, Fig. 2 is a circuit diagram showing the configuration of an embodiment of the present invention, and Fig. 3 is a circuit diagram showing an LC.
FIG. 4 is a diagram showing the gain and phase characteristic curves of the parallel resonant circuit. FIG. 4 is a diagram showing the individual and overall gain and phase characteristic curves of three LC parallel resonant circuits connected in series. FIG. 5 is the configuration of another embodiment of the present invention. FIG. F+~F3... Resonant circuit II~[3... Coil D+~D3... Variable capacitance diode Co I"Co 3... Capacitor patent applicant JEOL Ltd. agent Patent attorney Osamu Ijima Fuji

Claims (1)

[Claims] A plurality of resonant circuits including variable capacitance diodes whose resonance frequencies are shifted from each other are connected in series, and the amount of phase shift is changed by changing the control voltage applied to the variable capacitance diodes. A phase shift circuit characterized by: