Analog and digital signals are found in many high-frequency systems, which rely on the signal conversion capabilities of analog-to-digital converters (ADCs) and digital-to-analog converters (DACs) to process them. To their credit, suppliers of high-performance ADCs and DACs continue to push the clock speeds and performance levels of their converters, making them compatible with an increasing number of applications around the industry. These range from wired and wireless communications systems to the most advanced test-and-measurement equipment.

Not-so-ironically, some of the highest-performing data converters are available from the same companies that build test equipment, such as the 8-b TADC-1000 ADC module from Tektronix Component Solutions. The ADC board (Fig. 1) measures 3.6 x 5.9 x 1.5 in. It features an analog bandwidth of better than 8 GHz with sampling rates to 12.5 GSamples/s on one channel and 6.25 GSamples/s per channel on two channels. The digitizer module is designed for use with an external clock. It can work across a range of input clock frequencies from 1.60 to 3.125 GHz, to achieve sample rates from 8.0 to 12.5 GSamples/s in single-channel mode and 4.00 to 6.25 GSamples/s in dual-channel mode.

 

The TADC-1000 ADC module can stream data continuously at 100 Gb/s and maintain that streaming rate across the full bandwidth. The ADC achieves a high effective number of bits (ENOB) by means of onboard calibration. Built with devices based on the high-speed silicon germanium (SiGe) BiCMOS process from IBM, the firm’s application-specific-integrated-circuit (ASIC) design team interleaves four ADCs operating at 3.125 GSamples/s using advanced clocking techniques for synchronization. It is the same ASIC technology that has been used and proven in a number of the company’s high-performance test instruments. The digitizer module offers a spurious-free dynamic range (SFDR) of better than -47 dBc to 5 GHz with about 15 W power consumption.

Targeting the other side of data conversion, the firm also offers the model TDAC-2000 single-channel DAC, which is capable of operating to 12 GSamples/s. The 10-b DAC module features a single-ended CMOS parallel interface and can stream continuously at rates to 120 GSamples/s. The module consists of multiplexers and a high-speed DAC, with data supplied to the multiplexers via 320 data lines at 375 Mb/s, for the aggregate rate of 120 GSamples/s. The high-speed DAC is well suited for applications in electronic-warfare (EW) systems, radar systems, and in digital radio-frequency memories (DRFMs).

In terms of speed, Fujitsu Microelectronics Europe (FME) has set some data converter marks in recent years, having combined its CHArge-mode Interleaved Sampler technology (CHAIS) with standard 65-nm CMOS semiconductor process technology. The fabrication approach, unveiled in 2009, enabled the integration of multiple ADCs with signal-processing circuitry and memory on a single chip, nominally for high-speed coherent receivers in optical communications systems.

The 65-nm process has fabricated 8-b ADCs with sampling rates to 56 Gsamples/s per channel with only 2 W power consumption per channel, and with a half-speed mode of 28 Gsamples/s with only 1 W power consumption per channel. The converter approach works with a 1.75-GHz input reference clock, using internal multiplication to provide the required internal clock rates with low jitter. Earlier this year, Fujitsu Semiconductor Europe (FSEU) applied its 28-nm CMOS process to the development of low-power, 28-nm 8-b ADCs capable of supporting sampling rates from 55 to 70 GSamples/s with scalable analog bandwidths (Fig. 2).