The DAC5674 is a 14-bit resolution high-speed digital-to-analog converter (DAC) with integrated 4x-interpolation filter, on-board clock multiplier, and on-chip voltage reference. The device has been designed for high-speed digital data transmission in wired and wireless communication systems, high-frequency direct-digital synthesis (DDS) and waveform reconstruction in test and measurement applications.
The 4x-interpolation filter is implemented as a cascade of two 2x-interpolation filters, each of which can be configured for either low-pass or high-pass response. This enables the user to select one of the higher order images present at multiples of the input data rate clock while maintaining a low date input rate. The resulting high IF output frequency allows the user to omit the conventional first mixer in heterodyne transmitter architectures and directly up-convert to RF using only one mixer, thereby reducing system complexity and costs.
In 4x-interpolation low-pass response mode, the DACs excellent spurious free dynamic range (SFDR) at intermediate frequencies located in the first Nyquist zone (up to 40 MHz) allows for multicarrier transmission in cellular base transceiver stations (BTS). The low-pass interpolation mode thereby relaxes image filter requirements by filtering out the images in the adjacent Nyquist zones.
The DAC5674 PLL clock multiplier controls all internal clocks for the digital filters and DAC core. The differential clock input and internal clock circuitry provides for optimum jitter performance. Sine wave clock input signal is supported. The PLL can be bypassed by an external clock running at the DAC core update rate. The clock divider of the PLL ensures that the digital filters operate at the correct clock frequencies.
The DAC5674 operates from an analog supply voltage of 3.3 V and a digital supply voltage of 1.8 V. The digital I/Os are 1.8-V and 3.3-V CMOS compatible. Power dissipation is 500 mW at maximum operating conditions. The DAC5674 provides a nominal full-scale differential current-output of 20 mA, supporting both single-ended and differential applications. The output current can be directly fed to the load with no additional external output buffer required. The device has been specifically designed for a differential transformer coupled output with a 50- doubly terminated load. For a 20-mA full-scale output current both a 4:1 impedance ratio (resulting in an output power of 4 dBm) and 1:1 impedance ratio transformer (2-dBm output power) are supported. The latter configuration is preferred for optimum performance at high output frequencies and update rates.
An accurate on-chip 1.2-V temperature compensated bandgap reference and control amplifier allows the user to adjust the full-scale output current from 20 mA down to 2 mA. This provides 20-dB gain range control capabilities. Alternatively, an external reference voltage may be applied for maximum flexibility. The device features a SLEEP mode, which reduces the standby power to approximately 10 mW, thereby optimizing the power consumption for the systems need.
The DAC5674 is available in a 48-pin HTQFP Powerpad plastic quad flatpack package. The device is characterized for operation over the industrial temperature range of 40°C to 85°C.