MAX5894EGK+D【PDF 4/32 页】IC DAC 14BIT DUAL 500MSPS 68-QFN

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MAX5894

14-Bit, 500Msps, Interpolating and Modulating

Dual DAC with CMOS Inputs

______________________________________________________________________________________

Detailed Description

The MAX5894 dual, 500Msps, high-speed, 14-bit, cur-

rent-output DAC provides superior performance in

communication systems requiring low-distortion ana-

log-signal reconstruction. The MAX5894 combines two

DAC cores with 8x/4x/2x/1x programmable digital inter-

polation filters, a digital quadrature modulator, an SPI-

compatible serial interface for programming the device,

and an on-chip 1.20V reference. The full-scale output

current range is programmable from 2mA to 20mA to

optimize power dissipation and gain control.

Each channel contains three selectable interpolating fil-

ters making the MAX5894 capable of 1x, 2x, 4x, or 8x

interpolation, which allows for low input data rates and

high DAC update rates. When operating in 8x interpola-

tion mode, the interpolator increases the DAC conver-

sion rate by a factor of eight, providing an eight-fold

increase in separation between the reconstructed

waveform spectrum and its first image. The MAX5894

accepts either two’s complement or offset binary input

data format and can operate from either a single- or

dual-port input bus.

The MAX5894 includes modulation modes at fIM/2 and

fIM/4, where fIM is the data rate at the input of the modu-

lator. If 2x interpolation is used, this data rate is 2x the

input data rate. If 4x or 8x interpolation is used, this data

rate is 4x the input data rate. Table 1 summarizes the

modulator operating data rates for dual-port mode.

The power-down modes can be used to turn off each

DAC’s output current or the entire digital section.

Programming both DACs into power-down simultane-

ously automatically powers down the digital interpolator

filters. Note the SPI section is always active.

The analog and digital sections of the MAX5894 have

separate power-supply inputs (AVDD3.3, AVDD1.8,

AVCLK, DVDD3.3, and DVDD1.8), which minimize noise

coupling from one supply to the other. AVDD1.8 and

DVDD1.8 operate from a typical 1.8V supply, and all

other supply inputs operate from a typical 3.3V supply.

Serial Interface

The SPI-compatible serial interface programs the

MAX5894 registers. The serial interface consists of the

CS, DIN, SCLK, and DOUT. Data is shifted into DIN on

the rising edge of the SCLK when CS is low. When CS

is high, data presented at DIN is ignored and DOUT is

in high-impedance mode. Note:

CS must transition

high after each read/write operation. DOUT is the

serial data output for reading registers to facilitate easy

debugging during development. DIN and DOUT can

be connected together to form a 3-wire serial interface

bus or remain separate and form a 4-wire SPI bus.

The serial interface supports two-byte transfer in a

communication cycle. The first byte is a control byte

written to the MAX5894 only. The second byte is a data

byte and can be written to or read from the MAX5894.

Table 1. Quadrature Modulator Operating Data Rates (fIM is the Data Rate at the Input of

the Modulator) for Dual-Port Mode

INTERPOLATION RATE

MODULATION MODE (fLO)

MODULATION FREQUENCY

RELATIVE TO fDAC

MODULATION FREQUENCY

RELATIVE TO fDATA

fIM/2

fDAC/2

fDATA/2

fIM/4

fDAC/4

fDATA/4

fIM/2

fDAC/2

fDATA

fIM/4

fDAC/4

fDATA/2

fIM/2

fDAC/2

2 x fDATA

fIM/4

fDAC/4

fDATA

fIM/2

fDAC/4

2 x fDATA

fIM/4

fDAC/8

fDATA

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