AVDD

Current Source Array

S(1)

S(1)C

RLOAD

RLOAD

S(2)

S(2)C

S(N)

S(N)C

IOUT2

IOUT1

V

OUTDIFF +

(2

Code * 1023)

1024

I

OUTFS

R

LOAD

V

OUTDIFF +

V

OUT1 *

V

OUT2

DAC5652-EP

SGLS341C – JUNE 2006 – REVISED APRIL 2013

www.ti.com

The total differential output voltage is:

(7)

(8)

Analog Outputs

The DAC5652 provides two complementary current outputs, IOUT1 and IOUT2. The simplified circuit of the analog

output stage representing the differential topology is shown in Figure 18. 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 18. 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 DAC5652 (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 DAC5652 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 DAC5652 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.

Output Configurations

The current outputs of the DAC5652 allow for a variety of configurations. As mentioned previously, utilizing the

converter’s differential outputs yield the best dynamic performance. Such a differential output circuit may consist

of an RF transformer or a differential amplifier configuration. The transformer configuration is ideal for most

applications with ac coupling, while operational amplifiers are suitable for a dc coupled configuration.

18

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