THS5661 Datasheet, PDF (19/29 Pages) Texas Instruments – 12-BIT, 100 MSPS, CommsDACE DIGITAL-TO-ANALOG CONVERTER

IOUT1
IOUT2
50 Ω
+)
VOUT
–)
50 Ω
THS5661
12-BIT, 100 MSPS, CommsDAC™
DIGITAL-TO-ANALOG CONVERTER
SLAS200A – MAY 1999 – REVISED JULY 1999
APPLICATION INFORMATION
CFB
RFB
IOUT1
IOUT2
100 Ω
–
+
THS4001
THS4011
+)
VOUT
–)
(a)
(b)
Figure 27. Differential and Single-Ended Output Configuration
The THS5661 can be easily configured to drive a doubly terminated 50 Ω cable. Figure 28(a) shows the
single-ended output configuration, where the output current IOUT1 flows into an equivalent load resistance of
25 Ω. Node IOUT2 should be connected to ground or terminated with a resistor of 25 Ω. Differential-to-single
conversion (e.g., for measurement purposes) can be performed using a properly selected RF transformer, as
shown in Figure 28(b). This configuration provides maximum rejection of common-mode noise sources and
even order distortion components, thereby doubling the power to the output. The center tap on the primary side
of the transformer is connected to AGND, enabling a dc current flow for both IOUT1 and IOUT2. Note that the
ac performance of the THS5661 is optimum and specified using this differential transformer coupled output,
limiting the voltage swing at IOUT1 and IOUT2 to ±0.5 V.
IOUT1
50 Ω
IOUT2
25 Ω
VOUT
IOUT1
50 Ω
IOUT2
50 Ω
1:1
100 Ω
50 Ω
(a)
(b)
Figure 28. Driving a Doubly Terminated 50 Ω Cable
VOUT
50 Ω
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