Phase-Sensitive Detection. Part II: Quadrature Phase Detection

✍ Scribed by D. Traficante, Daniel

• Book ID: 102805120
• Publisher: John Wiley and Sons
• Year: 1990
• Tongue: English
• Weight: 741 KB
• Volume: 2
• Category: Article
• ISSN: 1043-7347
• DOI: 10.1002/cmr.1820020402

✦ Synopsis

The problems associated with the use of a single phase-sensitive detector (PSD) in an NMR receiver are reviewed. These problems can be eliminated by the use of two PSDs, arranged in parallel. The references to the PSDs are derived from a single source, but one is phase-shifted by 90" with respect to the other. This arrangement is called quadrature phase detection (QPD). The free-induction decays (FIDs) obtained as outputs from the two PSDs are phase-shifted by 90" with respect to one another, and are referred to as a "real" and an "imaginary" FID. The PSDs and the electronic components associated with them, including amplifiers and filters, are called the "real" and the "imaginary" channels. The FIDs from these channels can be processed so that the problems associated with the use of a single PSD are eliminated. In practice, however, a different set of problems emerges with the use of a QPD system because it is not possible to balance the two channels exactly. A procedure called CYCLOPS, which phase-cycles both the transmitter and the receiver portion of the computer, can be used to overcome these difficulties.