ADS58C48IPFPR datasheet(52/70 Pages) TI

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ADS58C48

SLAS689 – MAY 2010

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SNR ENHANCEMENT USING SNRBoost

SNRBoost 3G technology makes it possible to overcome SNR limitations due to quantization noise. Using

SNRBoost 3G, enhanced SNR can be obtained for any bandwidth (less than Nyquist or Fs/2). The SNR

improvement is achieved without affecting the default harmonic performance.

ADS58C48 uses 3rd generation SNRBoost technology (SNRBoost 3G) to achieve SNR enhancement over very

wide bandwidths (up to 60MHz). When SNRBoost 3G is enabled, the noise floor in the spectrum acquires a

typical bath-tub shape. The special feature of SNRBoost 3G is the nearly flat noise floor within the entire band of

the bath-tub.

The position of the center of the bath-tub and its bandwidth are programmable. The available bandwidths are 60

MHz, 40 MHz, 30 MHz and 20 MHz. Several center frequency options are available for each bandwidth.

ADS58C48 includes 55 pre-programmed combinations of center frequency and bandwidth. Any one of these

combinations can be selected by programming the register bits <Ch SNRBoost Filter #>. Each channel can be

programmed with independent center frequency and bandwidths.

One of the characteristics of SNRBoost 3G is that the bandwidth scales with the sampling frequency. 60-MHz and

40-MHz bandwidths are achieved at sampling rate of 184 MHz; at higher sample rates, even higher bandwidths

are possible .

The lower bandwidths 30 MHz and 20 MHz are achieved at sample rate of 200 MHz; at lower sample rates, the

achieved bandwidth will be lower. Table 10 shows all combinations of center frequency for each bandwidth,

specified as fraction of the sample rate.

By positioning the bath-tub within the desired signal band, SNR improvement can be achieved. Note that as the

bandwidth is increased, the amount of SNR improvement reduces.

After reset, the SNRBoost function is disabled.

Table 9. SNRBoost 3G Control Using SNRB Pins

VOLTAGE

APPLIED ON SNRB

SNRB_1

SNRB_2

PINS

LOW

SNRBoost 3G mode OFF for channels C and D

SNRBoost 3G mode OFF for channels A and B

HIGH

SNRBoost 3G mode ON for channels C and D

SNRBoost 3G mode ON for channels A and B

To use SNRBoost 3G with SNRB pins follow the exact sequence below:

Select and enable the SNRBoost 3G Filter

1. First, disable bits <DIGITAL MODE 1> and <DIGITAL MODE 2> (= 0)

2. Next, select the appropriate SNRBoost 3G filter using register bits <Ch SNRBoost Filter #>.

3. Finally, set bit <DIGITAL MODE 2> (= 1)

Turn On/OFF SNRBoost 3G

1. Use the SNRB1 and SNRB2 pins to dynamically turn on/off the SNRBoost 3G for each pair of channels.

Leave para for spacing

To use SNRBoost 3G without using SNRB pins follow the exact sequence below :

Select and enable the SNRBoost 3G Filter

1. First, disable bits <DIGITAL MODE 1> and <DIGITAL MODE 2> (= 0)

2. Next, select the appropriate SNRBoost filter using register bits <Ch SNRBoost Filter #>.

3. Finally, set bit <DIGITAL MODE 2> (= 1)

4. Set the SNRB pin over-ride bit <OVERRIDE SNRB pins>

Turn On/OFF SNRBoost 3G

1. Turn ON and OFF the SNRBoost 3G for each channel using the register bits <SNRBoost CH A ON>,

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