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, AV = 2
3.8nV/√Hz Total Noise, Low Distortion to 100MHz
LT1993-4
900MHz Low Distortion, Low Noise ADC Driver, AV = 4
2.4nV/√Hz Total Noise, Low Distortion to 100MHz
LT1993-10
700MHz Low Distortion, Low Noise ADC Driver, AV = 10
1.9nV/√Hz Total Noise, Low Distortion to 100MHz
LT1994
Low Noise, Low Distortion Fully Differential Ampler
70MHz Gain Bandwidth Differential In and Out
LT6402-6
300MHz Low Distortion, Low Noise ADC Driver, AV = 2
3.8nV/√Hz Input Referred Noise, Low Distortion to 30MHz
LT6553
650MHz Gain of 2 Triple Video Amplier
Triple Amplier with Fixed Gain
LT6554
650MHz Gain of 1 Triple Video Amplier
Triple Amplier with Fixed Gain
In cases where lowering the noise oor is paramount,
adding higher order lowpass or bandpass ltering can
signicantly increase signal-to-noise ratio. In Figure 13,
the LT6411 is shown driving an LTC2249 with a 2nd order
lowpass lter that has been carefully chosen to ensure
optimal intermodulation distortion. The response is
shown in Figure 14. The lter improves the SNR over the
unltered case by 6dB to 69.5dB. With the 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 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 2VP-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
–
+
55
80.6
80.6
5V
LT6411
390nH
LTC2249
390nH
55
10
AIN
–
AIN
+
10
15pF
6411 F13
IN+
IN–
1.9VDC
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
fIN = 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