Analog Circuits Cookbook

Direct Digital Synthesis 85

likely to be due to an image or alias. It results in both AM and PM, thus

hard limiting will convert the single spur into a pair of PM sidebands, each

6 dB lower than the original spur.

]

i

1

I

1

Figure

3.17 Noise reduction circuitry in the Q2334 can reduce the levels of

discrete line spurs at the expense of raising the general noise

floor.

(Reproduced

by courtesy of Qualcomm Inc. and Chronos Technology Ltd)

• OdB

-40 dB

-80 dB

CF:50MHz

Figure

3.18 Output of an SP2002 clocked at 400 MHz with bits 28 and 13 set

giving a demanded frequency of 50.001526 MHz (display centre frequency 50

MHz, span 100 kHz) (May, 1991) ...