DAC1405D750 6 © IDT 2012. All rights reserved.
Product data sheet Rev. 06 — 2 July 2012 13 of 41
Integrated Device Technology
DAC1405D750
Dual 14-bit DAC, up to 750 Msps; 4 and 8 interpolating
10. Application information
10.1 General description
The DAC1405D750 is a dual 14-bit DAC which operates at up to 750 Msps. Each DAC
consists of a segmented architecture, comprising a 6-bit thermometer sub-DAC and an
8-bit binary weighted sub-DAC.
The input data rate of up to 185 MHz combined with the maximum output sampling rate of
750 Msps make the DAC1405D750 extremely flexible in wide bandwidth and multi-carrier
systems. The device’s quadrature modulator and 32-bit NCO simplifies system frequency
selection. This is also possible because the 4 and 8 interpolation filters remove
undesired images.
A SYNC signal is provided to synchronize data when the PLL is in the off state.
Two modes are available for the digital input. In Dual-port mode, each DAC uses its own
data input line. In Interleaved mode, both DACs use the same data input line.
The on-chip PLL enables generation of the internal clock signals for the digital circuitry
and the DAC from a low speed clock. The PLL can be bypassed enabling the use of an
external, high-speed clock.
Each DAC generates two complementary current outputs on pins IOUTAP/IOUTAN and
IOUTBP/IOUTBN. This provides a full-scale output current (I
O(fs)
) up to 22 mA. An internal
reference is available for the reference current which is externally adjustable using pin
VIRES.
There are also some embedded features to provide an analog offset correction (auxiliary
DACs) and digital offset control as well as for gain adjustment. All the functions can be set
using the SPI.
The DAC1405D750 operates at both 3.3 V and 1.8 V each of which has separate digital
and analog power supplies. The digital input is 1.8 V and 3.3 V compliant and the clock
input is LVDS compliant.
10.2 Serial peripheral interface
10.2.1 Protocol description
The DAC1405D750 Serial Peripheral Interface (SPI) is a synchronous serial
communication port allowing easy interfacing with many industry microprocessors. It
provides access to the registers that define the operating modes of the chip in both write
and read modes.
This interface can be configured as a 3-wire type (SDIO as a bidirectional pin) or a 4-wire
type (SDIO and SDO as unidirectional pins, input and output port respectively). In both
configurations, SCLK acts as the serial clock and SCS_N acts as the serial chip select
bar. If several DAC1405D750 devices are connected to an application on the same
SPI-bus, only a 3-wire type can be used.
Each read/write operation is sequenced by the SCS_N signal and enabled by a LOW
assertion to drive the chip with 1 to 4 bytes, depending on the content of the instruction
byte (see Table 7).
