ADL5370

Rev. 0 | Page 14 of 20

RBIP

50Ω

RBIN

50Ω

93

92

19

20

IBBN

IBBP

AD9779

ADL5370

RBQN

50Ω

RBQP

50Ω

84

83

23

24

RSLI

100Ω

RSLQ

100Ω

OUT1_N

OUT1_P

OUT2_P

OUT2_N

QBBP

QBBN

LPI

2.7nH

LNI

2.7nH

1.1nF

C1I

1.1nF

C2I

LNQ

2.7nH

LPQ

2.7nH

1.1nF

C1Q

1.1nF

C2Q

Figure 32. DAC Modulator Interface with 3 MHz Third-Order Low-Pass Filter

USING THE AD9779 AUXILIARY DAC FOR CARRIER

FEEDTHROUGH NULLING

The AD9779 features an auxiliary DAC that can be used to

inject small currents into the differential outputs for each main

DAC channel. This feature can be used to produce the small

offset voltages necessary to null out the carrier feedthrough

from the modulator. Figure 33 shows the interface required

to utilize the auxiliary DACs. This adds four resistors to the

interface.

RBIP

50Ω

RBIN

50Ω

93

90

92

19

20

IBBN

IBBP

AD9779

ADL5370

RBQN

50Ω

RBQP

50Ω

84

87

89

83

86

23

24

RSLI

100Ω

RSLQ

100Ω

OUT1_N

AUX1_N

AUX2_N

OUT1_P

AUX1_P

OUT2_P

AUX2_P

OUT2_N

QBBP

QBBN

LPI

2.7nH

LNI

2.7nH

1.1nF

C1I

1.1nF

C2I

LNQ

2.7nH

LPQ

2.7nH

1.1nF

C1Q

1.1nF

C2Q

250Ω

500Ω

500Ω

500Ω

500Ω

250Ω

250Ω

250Ω

Figure 33. DAC Modulator Interface with Auxiliary DAC Resistors

GSM OPERATION

Figure 34 shows the GSM EVM and spectral mask performance

vs. output power for the ADL5370 at 450 MHz. For a given LO

amplitude, the performance is independent of output power.

–35

–56

–49

–42

–63

–70

–77

–84

–91

2.0

1.5

1.0

0.5

0

012345

67

OUTPUT POWER (dBm)

250kHz

400kHz

600kHz

1200kHz

Figure 34. GSM EVM and Spectral Performance vs. Channel Power at

450 MHz vs. Output Power; LO Power = 0 dBm

Figure 35 shows the GSM EVM, spectral mask performance

and 6 MHz offset noise vs. LO amplitude at 450 MHz with an

output power of 6 dBm. Increasing the LO drive level improves

the noise performance but degrades EVM performance.

–35

–56

–49

–42

–63

–70

–77

–84

–112

–105

–98

–91

3.1

2.9

2.7

2.5

2.3

2.1

1.9

1.7

1.5

1.3

1.1

0.9

–6

–4

–2

0246

LO AMPLITUDE (dBm)

250kHz

400kHz

600kHz

1200kHz

6 MHz OFFSET NOISE

Figure 35. GSM EVM, Spectral Performance, and 6 MHz Noise Floor vs.

LO Power at 450 MHz; Output Power = 6 dBm

Figure 35 illustrates that an LO amplitude of 0 dBm provides

the ideal operating point for noise and EVM for a GSM signal

at 450 MHz.