MCP37D11-80ESLASHTE datasheet(48/136 Pages) MICROCHIP

48 / 136 page

MCP37D11-80: 80 MSPS 12-BIT PIPELINED ADC

DS20006381A-page 48

 2020 Microchip Technology Inc.

4.8.2

NOISE-SHAPING REQUANTIZER

(NSR)

The device includes 11-bit and 12-bit digital

Noise-Shaping Requantizer (NSR) options. When this

function is enabled (see Register 5-33), output data is

requantized to 11-bit or 12-bit, respectively. The NSR

reshapes the requantization noise function and

pushes most of the noise outside the frequency band

of interest. As a result, the noise floor within the

selected bandwidth is substantially lower than that of a

typical 12-bit ADC.

To ensure the stability of the NSR, the input signal to

the NSR should be limited to less than -0.8 dBFS

(~90% of full scale). This can be achieved either by

limiting the analog input level or by adjusting the digital

gain control. See Section 4.9 “Digital Offset and

Digital Gain Settings” and Registers 5-63 to 5-70 for

details on the digital gain control. Input levels higher

than -0.8 dBFS may corrupt the NSR output and

should be avoided.

The NSR feature is available only for the single- and

dual-channel modes and can be independently

controlled per channel via the register settings. Two

NSRs are used:

• NSRA for channel A

• NSRB for channel B

In single-channel mode, only NSRA is used. In

dual-channel mode, both NSRA and NSRB are used:

NSRA is used for the first selected channel, and

NSRB is used for the second selected channel. Both

have 11-bit and 12-bit options. Each NSR block

consists of a series of filters which are selectable using

the NSRA<6:0> and NSRB<6:0> register bit settings.

Each filter is defined by a specific percentage

bandwidth and center frequency. The available

percentage bandwidths are:

• 11-bit mode: 22% and 25% of the sampling

frequency

• 12-bit mode: 25% and 29% of the sampling

frequency

The center frequency of the band is tunable such that

the frequency band of interest can be placed

anywhere within the Nyquist band. Table 4-12 lists all

the NSR-related registers. Equations 4-5 and 4-6

describe the NSR bandwidth of the 11-bit and 12-bit

options, respectively.

EQUATION 4-5:

NSR BANDWIDTH FOR

11-BIT OPTION

NSR represents the NSR filter number. See Tables 4-

13 and 4-14 for details.

EQUATION 4-6:

NSR BANDWIDTH FOR

12-BIT OPTION

NSR represents the NSR filter number. See Tables 4-

13 and 4-14 for details.

The center frequency of the band is tuned such that

the frequency spectrum of interest can be placed

anywhere within the Nyquist band. Figure 4-15 shows

a graphical demonstration of the NSR bandwidth,

which is a percentage of the ADC sampling frequency.

FIGURE 4-15:

Graphical demonstration of the

NSR filter’s transfer function. Note that fB is controlled

as a percentage of the sampling frequency (fS).

(a) 22% BW:

fCenter

----------------0.12

0.22

----------NSR



(b) 25% BW:

fCenter

----------------0.125

0.25

----------NSR 21

–





where 0

 NSR  20

where 21

 NSR  41

(a) 25% BW:

(b) 29% BW:

fCenter

----------------0.125

0.25

----------NSR 42

–





fCenter

----------------0.15

0.29

----------

NSR 63

–





where 42

 NSR  62

where 63

 NSR  76

MCP37D11-80E/TE Datasheet(PDF) 48 Page - Microchip Technology

MCP37D11-80E/TE Datasheet(HTML) 48 Page - Microchip Technology

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 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL