|
DAC900-Q1_15 Datasheet, PDF (16/29 Pages) Texas Instruments – 10-BIT 165-MSPS DIGITAL-TO-ANALOG CONVERTER | |||
|
◁ |
DAC900-Q1
SBAS505 â JUNE 2010
ADT1-1WT
(Mini-Circuits)
1:1
IOUT
RS
DAC900
Optional
RDIFF
50â¦
RL
IOUT
RS
50â¦
www.ti.com
Figure 3. Differential Output Configuration Using an RF Transformer
Differential Configuration Using an Op Amp
If the application requires a DC-coupled output, a difference amplifier may be considered, as shown in Figure 4.
Four external resistors are needed to configure the voltage-feedback op amp OPA680 as a difference amplifier
performing the differential to single-ended conversion. Under the shown configuration, the DAC900 generates a
differential output signal of 0.5Vp-p at the load resistors, RL. The resistor values shown were selected to result in
a symmetric 25Ω loading for each of the current outputs since the input impedance of the difference amplifier is
in parallel to resistors RL, and should be considered.
R2
402â¦
IOUT
DAC900
IOUT
R1
200â¦
CDIFF
R3
200â¦
OPA680
â5V +5V
VOUT
RL
26.1â¦
RL
28.7â¦
R4
402â¦
Figure 4. Difference Amplifier Provides Differential to Single-Ended Conversion and DC-Coupling
The OPA680 is configured for a gain of two. Therefore, operating the DAC900 with a 20mA full-scale output will
produce a voltage output of ±1V. This requires the amplifier to operate off of a dual power supply (±5V). The
tolerance of the resistors typically sets the limit for the achievable common-mode rejection. An improvement can
be obtained by fine tuning resistor R4.
This configuration typically delivers a lower level of ac performance than the previously discussed transformer
solution because the amplifier introduces another source of distortion. Suitable amplifiers should be selected
based on their slew-rate, harmonic distortion, and output swing capabilities. High-speed amplifiers like the
OPA680 or OPA687 may be considered. The ac performance of this circuit may be improved by adding a small
capacitor, CDIFF, between the outputs IOUT and IOUT, as shown in Figure 4. This will introduce a real pole to create
a low-pass filter in order to slewlimit the DACs fast output signal steps that otherwise could drive the amplifier
into slew-limitations or into an overload condition; both would cause excessive distortion. The difference amplifier
can easily be modified to add a level shift for applications requiring the single-ended output voltage to be
unipolar, i.e., swing between 0V and +2V.
16
Submit Documentation Feedback
Product Folder Link(s): DAC900-Q1
Copyright © 2010, Texas Instruments Incorporated
|
▷ |