Datasheet

TRF370317/

TRF370417

DAC3152/

DAC3162

IOUTAP

IOUTAN

IOUTBP

IOUTBN

Signal Conditioning

Quadrature modulator

out

~ 2.8 to 3.8 V

~ Varies

DAC3152

DAC3162

SLAS736D –NOVEMBER 2010–REVISED AUGUST 2012

www.ti.com

PASSIVE INTERFACE TO ANALOG QUADRATURE MODULATORS

A common application in communication systems is to interface the DAC to an IQ modulator like the TRF3703

family of modulators from Texas Instruments. The input of the modulator is generally of high impedance and

requires a specific common-mode voltage. A simple resistive network can be used to maintain 50-Ω load

impedance for the DAC3152/DAC3162 and also provide the necessary common-mode voltages for both the DAC

and the modulator.

Figure 43. DAC3152/DAC3162 to Analog Quadrature Modulator Interface

The DAC3152/DAC3162 has a maximum 20-mA full-scale output and a voltage compliance range of AVDD ± 0.5

V. The TRF3703 IQ modulator family has three common-mode voltage options: 1.5 V, 1.7 V, and 3.3 V, and the

TRF370417 IQ modulator has a 1.7-V common mode.

Figure 44 shows the recommended passive network to interface the DAC to the TRF370317, which has a

common-mode voltage of 1.7 V. The network generates the 3.3-V common mode required by the DAC output

and 1.7 V at the modulator input, while still maintaining a 50-Ω load for the DAC.

Figure 44. DAC3152/DAC3162 to TRF370317 or TRF370417 Interface

If V1 is set to 5 V and V2 is set to –5 V, the corresponding resistor values are R1 = 57 Ω, R2 = 80 Ω, and

R3 = 336 Ω. The loss developed through R2 is about –1.86 dB. When there is no –5-V supply available and V2

is set to 0 V, the resistor values are R1 = 66 Ω, R2 = 101 Ω, and R3 = 107 Ω. The loss with these values is

–5.76 dB.

Figure 45 shows the recommended network for interfacing with the TRF370333, which requires a common mode

of 3.3 V. This is the simplest interface, as there is no voltage shift. With V1 = 5 V and V2 = 0 V, the resistor

values are R1 = 66 Ω and R3 = 208 Ω.

Product Folder Links: DAC3152 DAC3162