AD9748ACP-PCB Analog Devices Inc, AD9748ACP-PCB Datasheet - Page 12

• Manufacturer Part Number: AD9748ACP-PCB
• Description: BOARD EVAL FOR AD9748ACP
• Manufacturer: Analog Devices Inc
• Series: TxDAC®r

Specifications of AD9748ACP-PCB

• Rohs Status: RoHS non-compliant
• Number Of Dac's: 1
• Number Of Bits: 8
• Outputs And Type: 1, Differential
• Sampling Rate (per Second): 210M
• Data Interface: Parallel
• Settling Time: 11ns
• Dac Type: Current
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Utilized Ic / Part: AD9748

AD9748
The control amplifier allows a wide (10:1) adjustment span of
I
μA and 625 μA. The wide adjustment span of I
several benefits. The first relates directly to the power
dissipation of the AD9748, which is proportional to I
the Power Dissipation section). The second relates to a 20 dB
adjustment, which is useful for system gain control purposes.
The small signal bandwidth of the reference control amplifier is
approximately 500 kHz and can be used for low frequency small
signal multiplying applications.
DAC TRANSFER FUNCTION
The AD9748 provides complementary current outputs, IOUTA
and IOUTB. IOUTA provides a near full-scale current output,
I
IOUTB, the complementary output, provides no current. The
current output appearing at IOUTA and IOUTB is a function of
both the input code and I
where DAC CODE = 0 to 255 (that is, decimal representation).
As mentioned previously, I
current I
V
where
The two current outputs typically drive a resistive load directly
or via a transformer. If dc coupling is required, then IOUTA
and IOUTB should be directly connected to matching resistive
loads, R
that R
IOUTA or IOUTB as would be the case in a doubly terminated
50 Ω or 75 Ω cable. The single-ended voltage output appearing
at the IOUTA and IOUTB nodes is simply
Note that the full-scale value of V
exceed the specified output compliance range to maintain
specified distortion and linearity performance.
OUTFS
OUTFS
REFIO
IOUTA = (DAC CODE/256) × I
IOUTB = (255 − DAC CODE)/256 × I
I
I
V
V
V
, when all bits are high (that is, DAC CODE = 255), while
OUTFS
REF
, and external resistor, R
over a 2 mA to 20 mA range by setting I
LOAD
OUTA
OUTB
DIFF
LOAD
= V
REF
= (IOUTA − IOUTB) × R
can represent the equivalent load resistance seen by
= 32 × I
= IOUTB × R
= IOUTA × R
, which is nominally set by a reference voltage,
, that are tied to analog common, ACOM. Note
REFIO
/R
REF
SET
LOAD
LOAD
OUTFS
OUTFS
SET
and can be expressed as:
is a function of the reference
. It can be expressed as:
OUTA
LOAD
OUTFS
and V
OUTFS
OUTB
REF
OUTFS
should not
between 62.5
provides
OUTFS
(see
Rev. A | Page 12 of 24
(1)
(2)
(3)
(4)
(5)
(6)
(7)
Substituting the values of IOUTA, IOUTB, I
expressed as:
Equation 7 and Equation 8 highlight some of the advantages of
operating the AD9748 differentially. First, the differential
operation helps cancel common-mode error sources associated
with IOUTA and IOUTB, such as noise, distortion, and dc
offsets. Second, the differential code dependent current and
subsequent voltage, V
voltage output (that is, V
signal power to the load.
Note that the gain drift temperature performance for a single-
ended (V
AD9748 can be enhanced by selecting temperature tracking
resistors for R
as shown in Equation 8.
ANALOG OUTPUTS
The complementary current outputs in each DAC, IOUTA,
and IOUTB can be configured for single-ended or differential
operation. IOUTA and IOUTB can be converted into
complementary single-ended voltage outputs, V
via a load resistor, R
Function section by Equation 5 through Equation 8. The
differential voltage, V
also be converted to a single-ended voltage via a transformer or
differential amplifier configuration. The ac performance
of the AD9748 is optimum and specified using a differential
transformer-coupled output in which the voltage swing at
IOUTA and IOUTB is limited to ±0.5 V.
The distortion and noise performance of the AD9748 can be
enhanced when it is configured for differential operation. The
common-mode error sources of both IOUTA and IOUTB can
be significantly reduced by the common-mode rejection of a
transformer or differential amplifier. These common-mode
error sources include even-order distortion products and noise.
The enhancement in distortion performance becomes more
significant as the frequency content of the reconstructed
waveform increases and/or its amplitude decreases. This is due
to the first-order cancellation of various dynamic common-
mode distortion mechanisms, digital feedthrough, and noise.
Performing a differential-to-single-ended conversion via a
transformer also provides the ability to deliver twice the
reconstructed signal power to the load (assuming no source
termination). Because the output currents of IOUTA and
IOUTB are complementary, they become additive when
processed differentially. A properly selected transformer allows
the AD9748 to provide the required power and voltage levels to
different loads.
V
(32 × R
DIFF
OUTA
= {(2 × DAC CODE − 255)/256}
LOAD
and V
LOAD
/R
SET
and R
OUTB
LOAD
) × V
DIFF
DIFF
OUTA
) or differential output (V
B
, as described in the DAC Transfer
SET
, is twice the value of the single-ended
, existing between V
REFIO
due to their ratiometric relationship,
or V
OUTB
), thus providing twice the
REF
OUTA
, and V
OUTA
DIFF
and V
and V
) of the
DIFF
OUTB
can be
OUTB
, can
(8)
,