AD6654/PCB Analog Devices Inc, AD6654/PCB Datasheet - Page 40

• Manufacturer Part Number: AD6654/PCB
• Description: BOARD EVALUATION FOR AD6654
• Manufacturer: Analog Devices Inc

Specifications of AD6654/PCB

• Module/board Type: Evaluation Board
• For Use With/related Products: AD6554
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

AD6654
control register bypasses this fixed coefficient HB filter. The
filter is useful only in certain filter configurations and bypassing
it for other applications results in power savings. For example,
the filter is useful in narrow-band applications in which more
filtering is required, as compared to wide-band applications, in
which a higher output rate might prohibit the use of a decimat-
ing filter. The response of the HB2 filter is shown in Figure 52.
The filter input sample rate is the same as the FIR2 filter output
rate and is given by one of the following equations:
where:
f
f
f
FIR2
HB2
HB1
–100.00
–110.00
–120.00
–19.99
–29.99
–39.99
–49.99
–60.00
–70.00
–80.00
–90.00
is the input rate of the HB1 filter.
–9.99
is the input rate of the HB2 filter.
is the input rate of the FIR2 filter.
0.01
f
f
HB2
HB2
Figure 52. HB2 Filter Response to the Input Rate of the Filter
0
= f
= f
FIR2
FIR2
0.1
= f
=
FRACTION OF HB2 INPUT SAMPLE RATE
0.2
HB1
f
HB1
2
, if HB1 is bypassed
0.3
, if HB1 is not bypassed
0.34
0.4
0.5
0.6
0.66
0.7
HB2 RESPONSE
0.8
0.9
–65
Rev. 0 | Page 40 of 88
The input to the filter has a maximum of 75 MHz. The
maximum output rate when not bypassed is 37.5 MHz.
The filter has a ripple of 0.00075 dB and rejection of 81 dB. For
an alias rejection of 81 dB, the alias-protected bandwidth is 33%
of the filter input sample rate. The bandwidth of the filter for a
ripple of 0.00075 dB is the same as alias-protected bandwidth,
due to the nature of half-band filters. The 3 dB bandwidth of
this filter is 47% of the filter input sample rate. For example, if
the sample rate into the filter is 25 MHz, then the alias-
protected bandwidth of the HB2 filter is 8.25 MHz (33% of
25 MHz). If the bandwidth of the required carrier is greater
than 8.25 MHz, then HB2 might not be useful.
Figure 53. Composite Response of FIR2 and HB2 Filters to Their Input Rates
–100.00
–110.00
–120.00
–19.99
–29.99
–39.99
–49.99
–60.00
–70.00
–80.00
–90.00
–9.99
0.01
0
0.1
FRACTION OF HB2 INPUT SAMPLE RATE
0.2
0.3
0.34
0.4
0.5
0.6
0.66
0.7
FIR2 + HB2
RESPONSE
0.8
0.9
–90