DAC348x + TRF3705 Filter Design and Gain Flatness

Prepared by Kang Hsia

09/23/2013

1

Gain Flatness Summary

• Gain flatness tested on DAC34H84 + TRF3705 with 350MHz LPF in between the DAC and modulator.

• Gain flatness of less than 1dB gain variation is observed.

• Gain flatness of the DAC and modulator is primarily due to the matching of the impedance between the DAC and modulator

2

TI DAC348x + TRF3705 Interface + BB Filter

3

3p3A3p3A

3p3A

-

+

VCCS1 1

-

+

VCCS2 1

IS1 10mA

IS2 10mA

-

+

-

+

VCVS1 10m

+

VG1

V1 3.3V

V+

VM1

Vdacp

Ioutp

Ioutn

Vdacn

R9

50O

hmR

8 50

Ohm

C1

4.6p

FC

2 4.

6pF

R6

8kO

hmR

7 8k

Ohm

R3

50O

hmR

1 50

Ohm

L1 33nH

L2 33nH

C4

2.7p

F

C5

8.7p

F

L3 33nH

L4 33nH

C7

2.7p

F

DAC Current Source TRF3705 Input Model

Frequency Response

4

T

Frequency (Hz)

10.00M 100.00M 1.00G

VM1

-29.67

-6.05

DAC Output / Modulator Input Connection

5

04/21/23

Gain Flatness Test Setup

• TSW3100 + TSW30H84 EVM

• 1228.8MSPS, 2x int

• Inv sinc enabled

• 2.7pF, 33nH, 8.7pF, 33nH, 2.7pF 5th order Butterworth 350MHz filter

04/21/23

TSW3100 GUI Setup

04/21/23

NCO Off (200MHz BW)

1 AP

CLRWR

A

Att 5 dB

*

3DB

RBW 100 kHz

VBW 300 kHz

SWT 30 ms

Ref -34 dBm

Start 1.8 GHz Stop 2.1 GHz30 MHz/

-44

-43

-42

-41

-40

-39

-38

-37

-36

-35

-341

Marker 1 [T1 ]

-34.79 dBm

1.800000000 GHz

Date: 30.NOV.2011 16:37:39

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NCO at 200MHz (200MHz BW)Filter roll-off = 350MHz (2150MHz RF)

Att 5 dB

A

1 AP

CLRWR

*

3DB

RBW 100 kHz

VBW 300 kHz

SWT 40 msRef -42 dBm

Start 1.8 GHz Stop 2.2 GHz40 MHz/

-52

-51

-50

-49

-48

-47

-46

-45

-44

-43

-42

1

Marker 1 [T1 ]

-45.76 dBm

1.900000000 GHz

Date: 30.NOV.2011 16:43:05

DAC output spectrum (corrected vs. uncorrected sinx/x roll-off)

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