Datasheet

DAC3152/

DAC3162

TRF370333/

TRF370317/

TRF370417

Filter

TRF370333

DAC3152/

DAC3162

DAC3152

DAC3162

www.ti.com

SLAS736D –NOVEMBER 2010–REVISED AUGUST 2012

Figure 45. DAC3152/DAC3162 to TRF370333 Interface

In most applications, a baseband filter is required between the DAC and the modulator to eliminate the DAC

images. This filter can be placed after the common-mode biasing network. For the DAC-to-modulator network

shown in Figure 46, R2 and the filter load R4 must be considered into the DAC impedance. The filter must be

designed for the source impedance created by the resistor combination of R3 || (R2 + R1). The effective

impedance seen by the DAC is affected by the filter termination resistor, resulting in R1 || (R2 + R3 || (R4/2)).

Figure 46. DAC to Modulator Interface With Filter

Factoring in R4 into the DAC load, a typical interface to the TRF370317 with V1 = 5 V and V2 = 0 V results in the

following values: R1 = 72 Ω, R2 = 116 Ω, R3 = 124 Ω and R4 = 150 Ω. This implies that the filter must be

designed for 75-Ω input and output impedance (single-ended impedance). The common-mode levels for the DAC

and modulator are maintained at 3.3 V and 1.7 V, and the DAC load is 50 Ω. The added load of the filter

termination causes the signal to be attenuated by –10.8 dB.

A filter can be implemented in a similar manner to interface with the TRF370333. In this case, it is much simpler

to balance the loads and common-mode voltages, due to the absence of R2. An added benefit is that there is no

loss in this network. With V1 = 5 V and V2 = 0 V, the network can be designed such that R1 = 115 Ω,

R3 = 681 Ω, and R4 = 200 Ω. This results in a filter impedance of R1 || R2 = 100 Ω, and a DAC load of R1 || R3

|| (R4/2), which is equal to 50 Ω. R4 is a differential resistor and does not affect the common-mode level created

by R1 and R3. The common-mode voltage is set at 3.3 V for a full-scale current of 20 mA.

For more information on how to interface the DAC3152/DAC3162 to an analog quadrature modulator, see the

application reports Passive Terminations for Current Output DACs (SLAA399) and Design of Differential Filters

for High-Speed Signal Chains (SLWA053).

Product Folder Links: DAC3152 DAC3162