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V

OUTDIFF +

V

OUT1 *

V

OUT2

(7)

V

OUTDIFF +

(2

Code * 16383)

16384

I

OUTFS

R

LOAD

(8)

Analog Outputs

AVDD

Current Source Array

S(1)

S(1)C

RLOAD

RLOAD

S(2)

S(2)C

S(N)

S(N)C

IOUT2

IOUT1

DAC5672-EP

SGLS339A – JUNE 2006 – REVISED OCTOBER 2006

APPLICATION INFORMATION (continued)

The total differential output voltage is:

The DAC5672 provides two complementary current outputs, IOUT1 and IOUT2. The simplified circuit of the analog

output stage representing the differential topology is shown in Figure 22. The output impedance of IOUT1 and

IOUT2 results from the parallel combination of the differential switches, along with the current sources and

associated parasitic capacitances.

Figure 22. Analog Outputs

The signal voltage swing that may develop at the two outputs, IOUT1 and IOUT2, is limited by a negative and

positive compliance. The negative limit of –1 V is given by the breakdown voltage of the CMOS process and

exceeding it compromises the reliability of the DAC5672 (or even causes permanent damage). With the

full-scale output set to 20 mA, the positive compliance equals 1.2 V. Note that the compliance range decreases

to about 1 V for a selected output current of IOUTFS = 2 mA. Care must be taken that the configuration of

DAC5672 does not exceed the compliance range to avoid degradation of the distortion performance and integral

linearity.

Best distortion performance is typically achieved with the maximum full-scale output signal limited to

approximately 0.5 VPP. This is the case for a 50-Ω doubly-terminated load and a 20-mA full-scale output current.

A variety of loads can be adapted to the output of the DAC5672 by selecting a suitable transformer while

maintaining optimum voltage levels at IOUT1 and IOUT2. Furthermore, using the differential output configuration in

combination with a transformer is instrumental for achieving excellent distortion performance. Common-mode

errors, such as even-order harmonics or noise, can be substantially reduced. This is particularly the case with

high output frequencies.

For those applications requiring the optimum distortion and noise performance, it is recommended to select a

full-scale output of 20 mA. A lower full-scale range of 2 mA may be considered for applications that require low

power consumption, but can tolerate a slight reduction in performance level.

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