CMOS 300 MSPS Quadrature Complete DDS
The AD9854 digital synthesizer is a highly integrated device that uses advanced DDS technology, coupled with two internal high speed, high performance quadrature DACs to form a digitally programmable I and Q synthesizer function. When referenced to an accurate clock source, the AD9854 generates highly stable, frequency-phase, amplitude-programmable sine and cosine outputs that can be used as an agile LO in communications, radar, and many other applications. The innovative high speed DDS core of the AD9854 provides 48-bit frequency resolution (1 μHz tuning resolution with 300 MHz SYSCLK). Maintaining 17 bits ensures excellent SFDR.
The circuit architecture of the AD9854 allows the generation of simultaneous quadrature output signals at frequencies up to 150 MHz, which can be digitally tuned at a rate of up to 100 million new frequencies per second. The sine wave output (externally filtered) can be converted to a square wave by the internal comparator for agile clock generator applications. The device provides two 14-bit phase registers and a single pin for BPSK operation.
For higher-order PSK operation, the I/O interface can be used for phase changes. The 12-bit I and Q DACs, coupled with the innovative DDS architecture, provide excellent wideband and narrow-band output SFDR. The Q DAC can also be configured as a user-programmable control DAC if the quadrature function is not desired. When configured with the comparator, the 12-bit control DAC facilitates static duty cycle control in high speed clock generator applications.
Two 12-bit digital multipliers permit programmable amplitude modulation, on/off output shaped keying, and precise amplitude control of the quadrature output. Chirp functionality is also included to facilitate wide bandwidth frequency sweeping applications. The programmable 4× to 20× REFCLK multiplier circuit of the AD9854 internally generates the 300 MHz system clock from an external lower frequency reference clock. This saves the user the expense and difficulty of implementing a 300 MHz system clock source.
Direct 300 MHz clocking is also accommodated with either single-ended or differential inputs. Single-pin conventional FSK and the enhanced spectral qualities of ramped FSK are supported. The AD9854 uses advanced 0.35 μm CMOS technology to provide a high level of functionality on a single 3.3 V supply.
The AD9854 is pin-for-pin compatible with the AD9852 single-tone synthesizer. It is specified to operate over the extended industrial temperature range of −40°C to +85°C.
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At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.
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Ask The Application Engineer—33: All About Direct Digital Synthesis
(Analog Dialogue, Vol. 38, August 2004)
Single-Sideband Upconversion of Quadrature DDS Signals to the...
(Analog Dialogue, Vol. 34, No. 3, May, 2000)
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