ADS62C17_1 Datasheet, PDF (46/67 Pages) Texas Instruments – Dual Channel 11 Bit, 200 MSPS ADC With SNRBoost

ADS62C17
SLAS631A – APRIL 2009 – REVISED JULY 2009 ............................................................................................................................................................. www.ti.com
0.1 mF
1:1
39 nH
0.1 mF
15 W
INP
50 W
0.1uF
25 W
50 W
22 pF
25 W
50 W
1:1
0.1 mF
39 nH
50 W
15 W
INM
VCM
Figure 46. Drive Circuit With Low Bandwidth (for low input frequencies)
The mismatch in the transformer parasitic capacitance (between the windings) results in degraded even-order
harmonic performance. Connecting two identical RF transformers back to back helps minimize this mismatch and
good performance is obtained for high frequency input signals. An additional termination resistor pair may be
required between the two transformers as shown in the figures. The center point of this termination is connected
to ground to improve the balance between the P and M sides. The values of the terminations between the
transformers and on the secondary side have to be chosen to get an effective 50Ω (in the case of 50Ω source
impedance).
0.1 mF
1:1
0.1 mF
0.1 mF ^{25 W}
5W
INP
50 W
1:1
0.1 mF
25 W
3.3 pF
50 W
INM
5W
VCM
Figure 47. Drive Circuit With High Bandwidth (for high input frequencies)
0.1μF
INP
0.1μF
25 Ω
0.1μF
T1
T2
25 Ω
INM
VCM
Figure 48. Drive circuit with very high bandwidth (> 300 MHz)
46
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