ADS58C48_14 Datasheet, PDF (62/71 Pages) Texas Instruments – Quad Channel IF Receiver with SNRBoost 3G

ADS58C48
SLAS689 – MAY 2010
www.ti.com
BOARD DESIGN CONSIDERATIONS
For EVM board information, refer to the ADS58C48 EVM User's Guide (SLAU313).
Grounding
A single ground plane is sufficient to give good performance, provided the analog, digital, and clock sections of
the board are cleanly partitioned. See the EVM User's Guide (SLAU313) for details on layout and grounding.
Exposed Pad
In addition to providing a path for heat dissipation, the pad is also electrically connected to analog and digital
ground internally. So, it is necessary to solder the exposed pad to the ground plane for best thermal and
electrical performance. For detailed information, see application notes.
DEFINITION OF SPECIFICATIONS
Analog Bandwidth – The analog input frequency at which the power of the fundamental is reduced by 3 dB with
respect to the low-frequency value.
Aperture Delay – The delay in time between the rising edge of the input sampling clock and the actual time at
which the sampling occurs. This delay is different across channels. The maximum variation is specified as
aperture delay variation (channel-to-channel).
Aperture Uncertainty (Jitter) – The sample-to-sample variation in aperture delay.
Clock Pulse Width/Duty Cycle – The duty cycle of a clock signal is the ratio of the time the clock signal remains
at a logic high (clock pulse width) to the period of the clock signal. Duty cycle is typically expressed as a
percentage. A perfect differential sine-wave clock results in a 50% duty cycle.
Maximum Conversion Rate – The maximum sampling rate at which specified operation is given. All parametric
testing is performed at this sampling rate unless otherwise noted.
Minimum Conversion Rate – The minimum sampling rate at which the ADC functions.
Differential Nonlinearity (DNL) – An ideal ADC exhibits code transitions at analog input values spaced exactly
1 LSB apart. The DNL is the deviation of any single step from this ideal value, measured in units of LSBs.
Integral Nonlinearity (INL) – The INL is the deviation of the ADC transfer function from a best fit line determined
by a least squares curve fit of that transfer function, measured in units of LSBs.
Gain Error – Gain error is the deviation of the ADC actual input full-scale range from its ideal value. The gain
error is given as a percentage of the ideal input full-scale range. Gain error has two components: error as a
result of reference inaccuracy and error as a result of the channel. Both errors are specified independently as
E_GREF and E_GCHAN.
To a first-order approximation, the total gain error is E_TOTAL ~ E_GREF + E_GCHAN.
For example, if E_TOTAL = ±0.5%, the full-scale input varies from (1 – 0.5/100) x FS_ideal to (1 + 0.5/100) x FS_ideal.
Offset Error – The offset error is the difference, given in number of LSBs, between the ADC actual average idle
channel output code and the ideal average idle channel output code. This quantity is often mapped into millivolts.
Temperature Drift – The temperature drift coefficient (with respect to gain error and offset error) specifies the
change per degree Celsius of the parameter from T_MIN to T_MAX. It is calculated by dividing the maximum deviation
of the parameter across the T_MIN to T_MAX range by the difference T_MAX – T_MIN.
Signal-to-Noise Ratio – SNR is the ratio of the power of the fundamental (P_S) to the noise floor power (P_N),
excluding the power at dc and the first nine harmonics.
SNR = 10Log^{10 PS}
P_N
(1)
SNR is either given in units of dBc (dB to carrier) when the absolute power of the fundamental is used as the
reference, or dBFS (dB to full-scale) when the power of the fundamental is extrapolated to the converter
full-scale range.
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