LMH6552 Datasheet, PDF (24/38 Pages) Texas Instruments – 1.5-GHz Fully Differential Amplifier

LMH6552
SNOSAX9I – APRIL 2007 – REVISED JANUARY 2015
www.ti.com
90
SFDR (dBc)
85
80
75
70
65
SNR (dBFs)
60
55
50
0 5 10 15 20 25 30 35 40
INPUT FREQUENCY (MHz)
Figure 50. LMH6552/ADC12DL080 SFDR and SNR Performance vs. Frequency
Figure 51 shows a combination circuit of the LMH6552 driving the ADC14DS105. The ADC14DS105 is a dual
channel 14-bit ADC with a sampling rate of 105 MSPS. The circuit in Figure 51 has a 2nd order low-pass LC
filter formed by the 620 nH inductor along with the 22-pF capacitor across the differential outputs of the
LMH6552. The filter has a pole frequency of about 50 MHz. Figure 52 shows the combined SFDR and SNR
performance over frequency with a −1 dBFs input signal and a sampling rate of 1000 MSPS.
50:
Single-Ended
AC-coupled
Source
68.1:
127:
49.9:
0.1 PF
127:
68.1:
274:
V⁺
ADC14DS105
100: ^{620 nH}
-+
14-Bit
LMH6552
+-
V^{- 100:}
22 pF
620 nH
105
MSPS
V_REF
274:
Figure 51. Driving a 14-bit ADC
The amplifier is configured to provide a gain of 2 V/V in a single-to-differential mode. The LMH6552 common
mode voltage is set by the ADC14DS105. Circuit testing is the same as described for the LMH6552 and
ADC12DL080 combination circuit. The 0.1-µF capacitor, in series with the 49.9-Ω resistor, is inserted to ground
across the 68.1Ω-resistor to balance the amplifier inputs.
24
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