LT6411 Datasheet, PDF (16/16 Pages) Linear Technology – 650MHz Differential ADC Driver/Dual Selectable Gain Amplifi er

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