LT6411
16
6411f
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2006
LT 0606 • PRINTED IN USA
RELATED PARTS
TYPICAL APPLICATION
PART NUMBER DESCRIPTION COMMENTS
LT1993-2 800MHz Low Distortion, Low Noise ADC Driver, A
V
= 2 3.8nV/√Hz Total Noise, Low Distortion to 100MHz
LT1993-4 900MHz Low Distortion, Low Noise ADC Driver, A
V
= 4 2.4nV/√Hz Total Noise, Low Distortion to 100MHz
LT1993-10 700MHz Low Distortion, Low Noise ADC Driver, A
V
= 10 1.9nV/√Hz Total Noise, Low Distortion to 100MHz
LT1994 Low Noise, Low Distortion Fully Differential Amplfi er 70MHz Gain Bandwidth Differential In and Out
LT6402-6 300MHz Low Distortion, Low Noise ADC Driver, A
V
= 2 3.8nV/√Hz Input Referred Noise, Low Distortion to 30MHz
LT6553 650MHz Gain of 2 Triple Video Amplifi er Triple Amplifi er with Fixed Gain
LT6554 650MHz Gain of 1 Triple Video Amplifi er Triple Amplifi er with Fixed Gain
In cases where lowering the noise fl oor is paramount,
adding higher order lowpass or bandpass fi ltering can
signifi cantly increase signal-to-noise ratio. In Figure 13,
the LT6411 is shown driving an LTC2249 with a 2nd order
lowpass fi lter that has been carefully chosen to ensure
optimal intermodulation distortion. The response is
shown in Figure 14. The fi lter improves the SNR over the
unfi ltered case by 6dB to 69.5dB. With the fi lter, the SNR
of the ADC and the LT6411 are comparable; better SNR
can be achieved by using either a higher resolution ADC
or additional fi ltering. Figure 15 shows the corresponding
SFDR of –75.5dBc with a 30MHz tone. Figure 16 shows
the 2-tone response of the LT6411 with 29.5MHz and
30.5MHz inputs. Note that 0dBFS corresponds to a 2V
P-P
differential signal.
Figure 13. Optimized 30MHz LT6411 Differential ADC Driver
Figure 15. SNR and SFDR of the LT6411 and Filter
Driving the LTC2249
Figure 16. 2-Tone Response of the LT6411 and Filter
Driving the LTC2249 at 29.5MHz, 30.5MHz
Figure 14. Frequency Response of the LT6411 and Filter
–
–
+
+
55Ω
80.6Ω
80.6Ω
5V
LT6411
390nH
LTC2249
390nH
55Ω
10Ω
A
IN
–
A
IN
+
10Ω
15pF
6411 F13
IN+
IN–
1.9V
DC
1.9V
DC
FREQUENCY (MHz)
0
–140
AMPLITUDE (dBFS)
–120
–100
–80
0
–40
5
15
20 40
6411 F15
–20
–60
–130
–110
–90
–10
–50
–30
–70
10
25
30 35
8192 POINT FFT
f
IN
= 30MHz, –1dBFS
SNR = 69.5dB
SFDR = 75.5dB
FREQUENCY (MHz)
1
0
GAIN (dB)
3
6
9
10 100 1000
6411 F14
–3
–6
–9
–12
FREQUENCY (MHz)
0
–140
AMPLITUDE (dBFS)
–120
–100
–80
0
–40
5
15
20 40
6411 F16
–20
–60
–130
–110
–90
–10
–50
–30
–70
10
25
30 35
32768 POINT FFT
TONE 1 AT 29.5MHz, –7dBFS
TONE 2 AT 30.5MHz, –7dBFS
IM3 = –89.7dBc
