PDF (double-sided) - Physics Department, UCSB - University of ...

described in Chapter 8 (specifically the Squid I/V measurement).
6.3.8 GHz DACs
The fiber-optical signals are sent to the FastBias and received from the PreAmp
cards by another custom electronic device, the GHz DAC. It is a high-speed
FPGA-based signal generator that uses two 14-bit DACs running at 1 GHz to
synthesize waveforms with frequencies up to 500 MHz. These waveforms are used
to control the RF portion of the qubit bias. This is done by compositing one
waveform that is directly synthesized by a DAC and another that is the result
of using the DACs to modulate a carrier microwave signal with an I/Q mixer.
The first half of the waveform generates Z-rotations and the measure pulse. The
second half of the waveform is used to generate X/Y-rotations. The GHz DAC
boards are controlled by a computer via a 100 MBit Ethernet connection and can
synchronize to each other via a 10 MHz reference clock and a daisy-chain trigger.
The GHz DACs as well as the bias cards could easily be replaced by off-theshelf
electronics, but the cost of the commercial equivalents would increase the
price of adding one more qubit channel by a factor of more than 20. This, and the
desire for exact control over the electronics’ performance, prompted us to design
these modules ourselves.
119