THS1060_05 Datasheet, PDF (17/22 Pages) Texas Instruments – 10-BIT 60 MSPS IF SAMPLING COMMUNICATIONS

THS1060
10-BIT 60 MSPS IF SAMPLING COMMUNICATIONS
ANALOG-TO-DIGITAL CONVERTER
SLAS212A – MARCH 2000 – REVISED MARCH 2001
APPLICATION INFORMATION
using the analog input
The THS1060 obtains optimum performance when the analog signal inputs are driven differentially. The circuit
below shows the optimum configuration, see Figure 23. The signal is fed to the primary of an RF transformer.
Since the input signal must be biased around the common mode voltage of the internal circuitry, the common
mode (V_CM) reference from the THS1060 is connected to the center-tap of the secondary. To ensure a steady
low noise V_CM reference the best performance is obtained when the V_CM output is connected to ground with
a 0.1 µF and 0.01 µF low inductance capacitor.
ac Signal
50 Ω
1:1
VIN+
T1-1T
R
THS1060
50 Ω
VIN–
VCM
0.01 µF
0.1 µF
Figure 23. THS1060 With Coaxial Feed
When it is necessary to buffer or apply a gain to the incoming analog signal, it is also possible to combine a
single-ended amplifier with an RF transformer as shown in Figure 24. For this application, a wide-band current
mode feedback amplifier such as the THS3001 is best. The single ended output allows the use of standard
passive filters between the amplifier output and the primary. In this case, the SFDR of the op amp is not as critical
as that of the A/D converter. While harmonics generated from within the A/D converter fold back into the first
Nyquist zone, harmonics generated externally in the op amps can be filtered out with passive filters.
1 kΩ
IF Input
RT
1 kΩ
_
10 Ω
+
THS3001
Impedance Ratio = 1:n
BPF
VIN+
THS1060
VIN_–
VCM
0.1 µF
0.01 µF
Figure 24. IF Input Buffered With THS3001 Op Amp
• POST OFFICE BOX 655303 DALLAS, TEXAS 75265
17