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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
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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)
10
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