STEL-1178A/CM

The STEL-1178A/CM is one member of the STEL-1178A series.It provides a compact, low-cost solution to applications requiring two independently controlled precision frequency sources. Separate registers control the functions of the two NCOs, making the device very easy to program. In the STEL-1178A the two NCOs also have independent 3-bit phase modulation, making the device suitable for phase modulation applications as well as making it possible to use an STEL-1178A as a quadrature synthesizer. The two NCOs also have independent clocks. The 12-bit outputs provide -75 dBc purity with suitable DACs, and DAC strobe outputs are also provided to simplify DAC timing.

Feature of the STEL-1178A is two completely independent 32-bit numerically controlled oscillators in a single package operating at up to 80 MHz.The STEL-1178A uses digital techniques to provide a cost-effective solution for low noise signal sources. The dual NCO features high frequency resolution with exceptional spectral purity of outputs up to 32 MHz. The device combines low power 1.5µ CMOS technology with a unique architectural design resulting in a power efficient, high-speed dual sinusoidal waveform generator able to achieve fine tuning resolution and exceptional spectral purity at clock frequencies up to 80 MHz. The dual NCO is designed to provide a simple interface to an 8-bit microprocessor bus.The phase noise of the NCO output signal may be determined from the phase noise of the clock signal input and the ratio of the output frequency to the clock frequency. This ratio squared times the phase noise power of the clock specified in a given bandwidth is the phase noise power that may be expected in that same bandwidth relative to the output frequency. Each NCO achieves its high operating frequency by making extensive use of pipelining in its architecture. The pipeline delays within the NCOs represent 16 clock edges. Note that when frequency changes occur at the outputs the changes are instantaneous, i.e., they occur in one clock cycle, with complete phase continuity.