Dual Track And Hold Chip For Ultra-Wideband Data Acquisition
The bandwidth of the RTH020, 9 GHz for 0.5 Vpp inputs and over 10 GHz for small signals, is more than three times that of any reported T/H and allows sampling of 1 GHz signals with 10 bit precision. The master-slave configuration of this dual T/H device holds the output signal for nearly an entire clock cycle, significantly easing the bandwidth requirements for subsequent circuitry, such as ADCs. With well under 1 mV noise and less than 100 fs aperture jitter, the RTH020 achieves a 56 dB signal-to-noise ratio and a-63 dB total harmonic distortion for a 500 MHz input signal at a full-scale power of 1 Vpp.
Direct conversion of multi-GHz carrier signals becomes a reality with the RTH020. Used in conjunction with existing ADCs, the T/H eliminates mixer and filter functions, lowering system cost by bringing the ADC closer to the antenna. "This device turns a moderate bandwidth commercial ADC into a 10-GHz bandwidth ADC," said Paul van der Wagt, Senior Scientist in RSC's High Speed Mixed Signal ICs department.
The RTH020's differential-in, differential-out dual T/H cascades two single T/H circuits, each of which is optimized for a separate function. The first T/H determines the dynamic performance, such as bandwidth, distortion, and jitter, of the entire part in sampled mode. The second T/H is optimized for low gain loss, distortion, and noise. Both T/H circuits used Schottky diode sampling bridges to yield high linearity and speed at the same time.
RTH020 packaged measurements show a small-signal bandwidth (< 0.1 Vpp input level) extending beyond 10 GHz. Large signal bandwidths are 9 and 6 GHz for 0.5 Vpp and 1 Vpp inputs, respectively. Says van der Wagt: "To detect weak signals, the small signal bandwidth is most relevant. Overall, the bandwidths of the RTH020 represent a 3x to 4x improvement over competing parts for comparable input levels." The part is designed for 10 bit distortion performance over the DC to 1 GHz band. For higher frequencies, performance gradually decreases to over 7.2 bits at 3 GHz (0.5 Vpp) and 6 bits at 5 GHz (0.25 Vpp), before showing gain roll-off.