JP2595412Y2 - Envelope feedback circuit - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an envelope feedback circuit, and more particularly to an envelope feedback circuit suitable for improving the linearity of an RF pulse output power amplifier of an MRI apparatus.

[0002]

2. Description of the Related Art FIG. 2 shows an example of a conventional envelope feedback circuit used for an RF pulse output section of an MRI apparatus. The envelope feedback circuit 51 includes a splitter 52 and a variable gain amplifier 55
, Balun 3, matching circuit 6, power FET 7
A, 7B, a matching circuit 8, a balun 9, a sampler 60, a positive amplitude side input signal detection circuit 11A, a positive amplitude side output signal detection circuit 12A, and a gain control circuit 13. Matching circuit 6 and power FET 7
A, 7B, the matching circuit 8, and the balun 9 constitute a power amplifier 20.

The positive amplitude side input signal detection circuit 11A extracts a positive amplitude input waveform from the input signal to the power amplifier 20 and outputs the same to the gain control circuit 13. The positive-amplitude-side output signal detection circuit 12A extracts a positive-amplitude output waveform from the output signal from the power amplifier 20 and
Output to The gain control circuit 13 compares the positive amplitude output waveform with the positive amplitude input waveform, and adjusts the gain of the variable gain amplifier 55 so that the envelopes match.

[0004]

In the conventional envelope feedback circuit 51, a variable gain amplifier is used so that the positive amplitude waveform of the output signal of the power amplifier 20 matches the positive amplitude waveform of the input signal to the power amplifier 20. 5
The gain of 5 is adjusted. Therefore, the power amplifier 2
Although there is no problem when the positive amplitude waveform and the negative amplitude waveform of the output signal from 0 are symmetric, the matching circuit 6 and the power FE
When the positive amplitude waveform and the negative amplitude waveform of the output signal become asymmetric due to imbalance such as T7A and 7B,
There is a problem that the envelope feedback is not properly performed for the negative amplitude.

It is an object of the present invention to provide an envelope feedback circuit that can appropriately apply envelope feedback even when the positive amplitude waveform and the negative amplitude waveform of the output signal of the power amplifier become asymmetric. is there.

[0006]

According to the envelope feedback circuit of the present invention, a variable gain amplifier for amplifying an input signal to a power amplifier is provided at a stage preceding the power amplifier, and an output signal from the power amplifier is combined with the input signal. A positive-amplitude-side input signal detection circuit for extracting a positive-amplitude input waveform from an input signal to the power amplifier, and an input to the power amplifier, wherein the envelope feedback circuit compares and adjusts the gain of the variable gain amplifier so that the envelopes match. A negative amplitude input signal detection circuit for extracting a negative amplitude input waveform from a signal, a positive amplitude output signal detection circuit for extracting a positive amplitude output waveform from an output signal of a power amplifier, and a negative amplitude output waveform from a power amplifier output signal Negative amplitude side output signal detection circuit and positive amplitude waveform of input signal to power amplifier A positive-amplitude variable gain amplifier that amplifies and outputs to a power amplifier; a negative-amplitude variable gain amplifier that amplifies a negative-amplitude waveform of an input signal to the power amplifier and outputs it to the power amplifier; A positive-amplitude-side gain control circuit that adjusts the gain of the positive-amplitude-side variable gain amplifier so that the envelope is matched with the positive-amplitude input waveform; and the envelope is compared by comparing the negative-amplitude output waveform with the negative-amplitude input waveform. And a negative-amplitude-side gain control circuit that adjusts the gain of the negative-amplitude-side variable gain amplifier so as to make the gain control.

In the envelope feedback circuit having the above configuration, it is preferable that the positive amplitude side variable gain amplifier and the negative amplitude side variable gain amplifier are configured by connecting a dual gate MOSFET to a push-pull.

[0008]

In the envelope feedback circuit of the present invention, the positive amplitude side input signal detection circuit, the positive amplitude side output signal detection circuit, the positive amplitude side gain control circuit, and the positive amplitude side variable gain amplifier are used to control the positive amplitude side. Apply envelope feedback. Further, a negative amplitude side envelope feedback is applied by a negative amplitude side input signal detection circuit, a negative amplitude side output signal detection circuit, a negative amplitude side gain control circuit, and a negative amplitude side variable gain amplifier. That is,
Envelope feedback is separately applied to the positive amplitude side and the negative amplitude side. Therefore, even when the positive amplitude waveform and the negative amplitude waveform of the output signal of the power amplifier become asymmetric, it is possible to appropriately apply the envelope feedback to the positive amplitude and the negative amplitude.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail with reference to the embodiment shown in the drawings. Note that this does not limit the present invention.

FIG. 1 is a circuit diagram of an embodiment of the envelope feedback circuit of the present invention. The envelope feedback circuit 1 includes a splitter 2 and a balun 3
, A matching circuit 4 and a positive amplitude side variable gain amplifier 5
A, negative amplitude side variable gain amplifier 5B, matching circuit 6, power FETs 7A and 7B, matching circuit 8
A balun 9, a sampler 10, a positive amplitude side input signal detection circuit 11A, a positive amplitude side output signal detection circuit 12A,
It includes a positive amplitude side gain control circuit 13A, a negative amplitude side input signal detection circuit 11B, a negative amplitude side output signal detection circuit 12B, and a negative amplitude side gain control circuit 13B. The matching circuit 6, the power FETs 7A and 7B, the matching circuit 8, and the balun 9 constitute a power amplifier 20. The positive amplitude side variable gain amplifier 5A and the negative amplitude side variable gain amplifier 5B are configured by connecting a dual gate MOSFET to a push-pull.

The positive amplitude side input signal detection circuit 11A extracts a positive amplitude input waveform from the input signal to the power amplifier 20, and outputs the waveform to the positive amplitude side gain control circuit 13A. The positive-amplitude-side output signal detection circuit 12A extracts a positive-amplitude output waveform from the output signal from the power amplifier 20, and outputs it to the positive-amplitude-side gain control circuit 13A. The positive amplitude side gain control circuit 13A compares the positive amplitude output waveform with the positive amplitude input waveform, and adjusts the gain of the positive amplitude side variable gain amplifier 5A so that the envelopes match.

On the other hand, the negative amplitude side input signal detection circuit 11B
Extracts a negative amplitude input waveform from the input signal to the power amplifier 20 and outputs it to the negative amplitude side gain control circuit 13B. The negative amplitude side output signal detection circuit 12B extracts a negative amplitude output waveform from the output signal from the power amplifier 20,
It outputs to the negative amplitude side gain control circuit 13B. The negative amplitude side gain control circuit 13B compares the negative amplitude output waveform with the negative amplitude input waveform, and adjusts the gain of the negative amplitude side variable gain amplifier 5B so that the envelopes match.

As described above, according to the envelope feedback circuit 1, since the envelope feedback is separately applied to the positive amplitude side and the negative amplitude side, the positive amplitude waveform and the negative amplitude waveform of the output signal of the power amplifier 20 are provided. Can be appropriately applied to the positive amplitude and the negative amplitude even when the signal becomes asymmetric.

[0014]

According to the envelope feedback circuit of the present invention, since the envelope feedback is separately applied to the positive amplitude side and the negative amplitude side, the positive amplitude waveform and the negative amplitude waveform of the output signal of the power amplifier become asymmetric. In this case, the envelope feedback can be appropriately applied to the positive amplitude and the negative amplitude. Therefore, when used for the output unit of the RF pulse of the MRI apparatus,
There is an effect that the pulse waveform becomes appropriate and the slice profile can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of an envelope feedback circuit of the present invention.

FIG. 2 is a circuit diagram of an example of a conventional envelope feedback circuit.

[Explanation of symbols]

 Reference Signs List 1 envelope feedback circuit 5A positive amplitude side variable gain amplifier 5B negative amplitude side variable gain amplifier 11A positive amplitude side input signal detection circuit 11B negative amplitude side input signal detection circuit 12A positive amplitude side output signal detection circuit 12B negative amplitude side output signal detection circuit 13A Positive amplitude side gain control circuit 13B Negative amplitude side gain control circuit 20 Power amplifier

Claims (2)

(57) [Scope of request for utility model registration] 1. A variable gain amplifier for amplifying an input signal to a power amplifier is provided in a stage preceding the power amplifier, an output signal from the power amplifier is compared with the input signal, and the variable gain amplifier is adjusted so as to match an envelope. In the envelope feedback circuit that adjusts the gain of the amplifier, a positive amplitude side input signal detection circuit that extracts the positive amplitude input waveform from the input signal to the power amplifier, and a negative amplitude side input that extracts the negative amplitude input waveform from the input signal to the power amplifier A signal detector, a positive-amplitude output signal detector that extracts a positive-amplitude output waveform from the output signal of the power amplifier, a negative-amplitude output signal detector that extracts a negative-amplitude output waveform from the output signal of the power amplifier, and a power amplifier A positive-amplitude variable gain amplifier that amplifies the positive-amplitude waveform of the input signal of A negative-amplitude variable-gain amplifier that amplifies a negative-amplitude waveform of an input signal to the power amplifier and outputs the amplified signal to the power amplifier; and compares the positive-amplitude output waveform with the positive-amplitude input waveform to match the envelope. A positive-amplitude-side gain control circuit for adjusting the gain of the negative-side variable gain amplifier; and a negative-gain control circuit for comparing the negative-amplitude output waveform with the negative-amplitude input waveform and adjusting the gain of the negative-amplitude variable gain amplifier so that the envelopes match. An envelope feedback circuit comprising: an amplitude-side gain control circuit. 2. The envelope feedback circuit according to claim 1, wherein said positive amplitude side variable gain amplifier and said negative amplitude side variable gain amplifier are configured by connecting a dual gate MOSFET to a push-pull. Envelope feedback circuit.