AD6636PCB datasheet(30/72 Pages) AD

30 / 72 page

AD6636

Rev. 0 | Page 30 of 72

This filter runs at the same sample rate as the CIC filter output

rate and is given by

cic

FIR

where:

fin is the input rate in to the channel.

MCIC is the decimation ratio in the CIC filter stage.

The maximum input and output rates for this filter are

150 MHz.

Decimate-by-2 Half-Band Filter (HB1)

The next stage of the FIR-HB block is a decimate-by-2 half-

band filter. The 11-tap, symmetrical, fixed-coefficient HB1 filter

has low power consumption due to its polyphase implementa-

tion. The filter has 22 bits of input and output data with 10-bit

coefficients. Table 14 lists the coefficients of the half-band filter.

The normalized coefficients used in the implementation and

the 10-bit decimal equivalent value of the coefficients are also

listed. Other coefficients are zeros.

Table 14. Fixed Coefficients for HB1 Filter

Coefficient

Number

Normalized

Coefficient

Decimal Coefficient

(10-Bit)

C1, C11

0.013671875

C3, C9

−0.103515625

−53

C5, C7

0.58984375

302

512

Similar to the FIR1 filter, this filter can be used or bypassed.

Writing Logic 0 to the HB1 enable bit in the FIR-HB control

useful only in certain filter configurations and bypassing it for

other applications results in power savings. For example, it is

useful in narrow-band and wideband output applications in

which more filtering is required as compared to very wide

bandwidth applications in which a higher output rate might

prohibit the use of a decimating filter. The response of the filter

is shown in Figure 32.

The input sample rate of this filter is the same as the CIC filter

output rate and is given by

cic

where:

fin is the input rate in to the channel.

MCIC is the decimation ratio in the CIC filter stage.

FRACTION OF HB1 INPUT SAMPLE RATE

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

110

100

120

HB1 RESPONSE

0.43

0.57

–77

Figure 32. HB1 Filter Response to the Input Rate of the Filter

The filter has a maximum input sample rate of 150 MHz

and, when filter is not bypassed, the maximum output rate is

75 MHz.

The filter has a ripple of 0.0012 dB and rejection of 77 dB. For

an alias rejection of 77 dB, the alias-protected bandwidth is 14%

of the filter input sample rate. The bandwidth of the filter for a

ripple of 0.00075 dB is also the same as the alias-protected

bandwidth, due to the nature of half-band filters. The 3 dB

bandwidth of this filter is 44% of the filter input sample rate.

For example, if the sample rate into the filter is 50 MHz, then

the alias-protected bandwidth of the HB1 filter is 7 MHz. If the

bandwidth of the required carrier is greater than 7 MHz, then

HB1 might not be useful.

FRACTION OF HB1 INPUT SAMPLE RATE

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

–20

–10

–40

–30

–60

–50

–80

–70

–100

–90

–120

–110

–107

FIR1 + HB1 RESPONSE

0.43

0.57

Figure 33. Composite Response of FIR1 and HB1 Filters to Their Input Rate

AD6636PCB датащи(PDF) 30 Page - Analog Devices

AD6636PCB датащи(HTML) 30 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72

датащи скачать

ссылки URL