Power amplifier for use in an NMR tomography apparatus

• US 6,034,565 A
• Filed: 07/21/1998
• Issued: 03/07/2000
• Est. Priority Date: 07/23/1997
• Status: Expired due to Fees

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Schweighofer, Peter
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): Nguyen, Patricia
• Application Number:
  US09/119,969
• Time in Patent Office: 595 Days
• Field of Search: 330/10, 330/207 A, 330/251
• US Class Current: 330/10
• CPC Class Codes: G01R 33/3852 Gradient amplifiers; means for controlling the application of a gradient magnetic field to the sample, e.g. a gradient signal synthesizer
• CPC Class Codes: H02M 5/458 using semiconductor devices only
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A power amplifier has an amplifier assembly and a resonant assembly with a resonant capacitor and a control element. A parallel resonant circuit can be formed by the resonant capacitor and a load that can be connected to the amplifier. An output voltage or an intermediate circuit voltage of the amplifier can be applied at the resonance capacitor via the control element. An NMR tomography apparatus has at least one such power amplifier. The power amplifier can be universally used with low components outlay and is able to generate a number of signal forms.

Claims

1. A power amplifier comprising:

an amplifier assembly forming a voltage source;

a resonant assembly connected in parallel across said amplifier assembly, said resonant assembly comprising a resonant capacitor and a control element connected in series; and

said amplifier assembly being operable for generating an output voltage of said power amplifier in a non-resonant mode of said power amplifier, and said resonant assembly being operable for generating said output voltage of said power amplifier in a resonant mode of said power amplifier.

2. A power amplifier as claimed in claim 1 wherein said amplifier assembly comprises a switched output stage comprising means for producing a switched output stage voltage by pulse-width modulation in said non-resonant mode.

3. A power amplifier as claimed in claim 2 comprising filtering means for filtering said switched output stage voltage, said filtering means being active only in said non-resonant mode.

4. A power amplifier as claimed in claim 2 comprising filtering means for filtering said switched output stage voltage, said filtering means being active only in said resonant mode.

5. A power amplifier as claimed in claim 2 comprising filtering means for filtering said switched output stage voltage, said filtering means being active both in said non-resonant and resonant modes.

6. A power amplifier as claimed in claim 1 having a pair of output terminals with said output voltage being across said pair of output terminals, said output terminals being connectable directly to a load without insertion of any other components.

7. A power amplifier as claimed in claim 2 further comprising control means for driving said control element and for driving said switched output stage.

8. A power amplifier comprising:

an intermediate circuit assembly which generates an intermediate circuit voltage;

a resonant assembly comprising a resonant capacitor and a control element connected across said intermediate circuit voltage, said control element being operable to connect and disconnect said resonant capacitor across said intermediate circuit voltage; and

a switched output stage connected across said resonant capacitor, said switched output stage comprising means, in a first mode, for producing a switched output stage voltage by pulse-width modulation of said intermediate circuit voltage, said switched output stage voltage being employed for generating an output voltage, and, in a second mode, for forming a parallel resonant circuit between said resonant capacitor and a load.

9. A power amplifier as claimed in claim 8 wherein in said first mode said intermediate circuit voltage is across said resonant capacitor and in said second mode said intermediate circuit voltage is disconnected from said resonant capacitor by said control element.

10. A power amplifier as claimed in claim 8 wherein said switched output stage comprises means for conducting a resonant current in said second mode.

11. A power amplifier as claimed in claim 8 comprising means for pre-charging said resonant capacitor to said intermediate circuit voltage in a third mode.

12. A power amplifier as claimed in claim 8 having a pair of output terminals with said output voltage being across said pair of output terminals, said output terminals being connectable directly to a load without insertion of any other components.

13. A power amplifier as claimed in claim 8 wherein said control element comprises an IGBT connected in a shunt arm of a diode bridge.

14. A power amplifier as claimed in claim 8 wherein said control element comprises two IGBTs connected in parallel with opposite polarity.

15. A power amplifier as claimed in claim 8 comprising filtering means for filtering said switched output stage voltage, said filtering means being active only in said first mode.

16. A power amplifier as claimed in claim 8 comprising filtering means for filtering said switched output stage voltage, said filtering means being active only in said second mode.

17. A power amplifier as claimed in claim 8 comprising filtering means for filtering said switched output stage voltage, said filtering means being active both in said first and second modes.

18. A power amplifier as claimed in claim 8 further comprising control means for driving said control element and for driving said switched output stage.

19. A power amplifier comprising:

an amplifier assembly forming a voltage source;

a resonant assembly connected in parallel across said amplifier assembly forming a voltage source, said resonant assembly comprising a resonant capacitor and a control element connected in series;

said amplifier assembly and said resonant assembly, in combination, comprising means for generating an output voltage; and

said control element being a control element selected from the group consisting of an IGBT connected in a shunt arm of a diode bridge, and two IGBTs connected in parallel with opposite polarity.