AD9240AS Analog Devices Inc, AD9240AS Datasheet - Page 21

• Manufacturer Part Number: AD9240AS
• Description: IC ADC 14BIT 10MSPS 44-MQFP
• Manufacturer: Analog Devices Inc

Specifications of AD9240AS

• Mounting Type: Surface Mount
• Rohs Status: RoHS non-compliant
• Number Of Bits: 14
• Sampling Rate (per Second): 10M
• Data Interface: Parallel
• Number Of Converters: 7
• Power Dissipation (max): 330mW
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 44-MQFP, 44-PQFP
• Power Dissipation Pd: 330mW
• Input Channels Per Adc: 2
• No. Of Channels: 2
• Peak Reflow Compatible (260 C): No
• Sample Rate: 10MSPS
• Supply Voltage Max: 5V
• No. Of Bits: 14 Bit
• For Use With: AD9240-EB - BOARD EVAL FOR AD9240
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

the bandlimited IF signal aliases back into the center of the ADC’s
baseband region (i.e. F
image of the IF signal centered at 37.5 MHz will be aliased back
to 2.5 MHz which corresponds to one quarter of the sample rate
(i.e. F
frequency inversion that may easily be corrected for in the digital
domain.
To maximize its distortion performance, the AD9240 is config-
ured in the differential mode using a transformer. Preceding the
AD9240 is a bandpass filter and a 32 dB gain stage. A large
gain stage may be required to compensate for the high insertion
losses of a SAW filter used for image rejection. The gain stage
will also provide adequate isolation for the SAW filter from the
transient currents associated with AD9240’s input stage.
The gain stage can be realized using one or two cascaded AD8009
op amps. The AD8009 is a low cost current-feedback op amp
having a third order intercept of 33 dB for a gain of +10 MHz
at 37.5 MHz. A passive bandpass filter is required after the
AD8009 to reduce the resulting second order distortion prod-
ucts and limit its out-of-band noise. The specifications of this
filter are application dependent and will affect both the total
distortion and noise performance of this circuit.
Figure 53 shows the single-tone SNR and SFDR performance of
the AD9240 configured in the 2 V and 5 V span without using
the AD8009 gain stage. Only a slight degradation in SNR perfor-
mance (i.e., 1 dB) was noted with the inclusion of the AD8009
gain stage and a bandpass filter. Note, the tradeoff in SNR and
SFDR (dBFS) performance between the 5 V and 2 V spans at
different signal levels.
REV.
SAW FILTER
OUTPUT
50
Figure 52. Simplified AD9240 IF Sampling Circuit
B
S
/4). Note, the IF signal in this case will have undergone a
22.1
AD8009
G
1
200
= 20dB
50
S
93.1
/4). At a sample rate of 10 MSPS, an
AD8009
G
2
280
= 12dB
50
MINI-CIRCUITS
T4-6T
200
0.1 F
AD9240
VINA
CML
VINB
–21–
Figure 54 compares the two tone SFDR performance of the
AD9240 in the 2 V span with and without the use of the AD8009
gain stage. No degradation in distortion performance was noted
with the inclusion of the AD8009 gain stage provided that the
AD8009 2nd order distortion products are sufficiently attenu-
ated by the bandpass filter.
Figure 53. Single-Tone SNR/SFDR vs. Input Amplitude
@ 37.45 MHz
Figure 54. Two Tone SFDR vs. Input Amplitude
@ f
1
100
80
70
60
50
40
30
20
10
90
80
70
60
50
40
30
20
10
= 36.40 MHz and f
0
–80
0
–90
w/AD8009 – dBFS
–80
SFDR w/2V SPAN
–70
w/o AD8009 – dBc
SFDR w/5V SPAN
–70
INPUT POWER LEVEL (f
–60
INPUT POWER LEVEL – dBFS
–60
–50
w/AD8009 – dBc
2
–50
= 38.60 MHz
w/o AD8009 – dBFS
SNR w/2V SPAN
–40
–40
85 dB REFERENCE LINE
1
–30
= f
–30
2
SNR w/5V SPAN
) – dBFS
–20
–20
AD9240
–10
–10
0
0