Direct Digital-Frequency Synthesis by Analog Interpolation

A highly compact 9-bit CMOS direct digital synthesizer without read-only memory that consumes 8 muW/MHz is described. The circuit is based upon a small nonlinear array of six current sources and six current switches. This array converts an analog voltage that represents the signal phase to an output current that represents the corresponding amplitude. Measurement results show that the resulting 3.3-V 0.35-mum system is robust to mismatch and capable of generating a signal with a spurious free dynamic range as good as -48 dBc with a circuit area of 0.0085mm
²
. This level of performance and the compactness of the analog circuit make it an attractive starting point for the arrays of frequency synthesizers that will be needed in a range of instrumentation systems