AD9857/PCB Analog Devices Inc, AD9857/PCB Datasheet - Page 19

• Manufacturer Part Number: AD9857/PCB
• Description: BOARD EVAL FOR AD9857
• Manufacturer: Analog Devices Inc

Specifications of AD9857/PCB

• Rohs Status: RoHS non-compliant
• Module/board Type: Evaluation Board
• For Use With/related Products: AD9857
• Lead Free Status / Rohs Status: Not Compliant

Table 5. Parallel Data Bus Timing
Symbol
t
t
INVERSE CIC FILTER
The inverse cascaded integrator comb (CIC) filter precompen-
sates the data to offset the slight attenuation gradient imposed
by the CIC filter. See the Programmable (2× to 63×) CIC
Interpolating Filter section. The I (or Q) data entering the first
half-band filter occupies a maximum bandwidth of one-half
f
input of the first half-band filter). This is shown graphically in
Figure 23.
DATA
DS
DH
as defined by Nyquist (where f
TxENABLE
TxENABLE
INBAND
ATTENUATION
GRADIENT
D<13:0>
D<13:0>
PDCLK
PDCLK
f
DATA
/2
Definition
Data Setup Time
Data Hold Time
f
DATA
Figure 23. CIC Filter Response
CIC FILTER RESPONSE
t
t
DS
DS
t
t
DS
DS
DATA
Figure 21. 14-Bit Parallel Port Timing Diagram—Quadrature Modulation Mode
I
I
0
0
t
t
Figure 22. 14-Bit Parallel Port Timing Diagram—Interpolating DAC Mode
DH
DH
is the sample rate at the
Minimum
4 ns
0 ns
4f
DATA
Q
I
1
0
f
Rev. C| Page 19 of 40
I
I
1
2
If the CIC filter is employed, the inband attenuation gradient
could pose a problem for those applications requiring an
extremely flat pass band. For example, if the spectrum of the
data as supplied to the AD9857 I or Q path occupies a
significant portion of the one-half f
frequencies of the data spectrum receives slightly more
attenuation than the lower frequencies (the worst-case overall
droop from f = 0 to one-half f
acceptable in certain applications. The inverse CIC filter has a
response characteristic that is the inverse of the CIC filter
response over the one-half f
The net result is that the product of the two responses yields in
an extremely flat pass band, thereby eliminating the inband
attenuation gradient introduced by the CIC filter. The price
to be paid is a slight attenuation of the input signal of approx-
imately 0.5 dB for a CIC interpolation rate of 2 and 0.8 dB for
interpolation rates of 3 to 63.
The inverse CIC filter is implemented as a digital FIR filter
with a response characteristic that is the inverse of the
programmable CIC interpolator. The product of the two
responses yields a nearly flat response over the baseband
Nyquist bandwidth. The inverse CIC filter provides frequency
compensation that yields a response flatness of ±0.05 dB over
the baseband Nyquist bandwidth, allowing the AD9857 to
provide excellent SNR over its performance range.
The inverse CIC filter can be bypassed by setting Control
Register 06h<0>. It is automatically bypassed if the CIC
interpolation rate is 1×. Whenever this stage is bypassed, power
to the stage is shutoff, thereby reducing power dissipation.
Q
I
3
1
DATA
I
K – 1
DATA
I
N
region.
is < 0.8 dB). This may not be
DATA
t
t
DH
DH
region, the higher
Q
I
K
N
AD9857