9.1.1 Specification Definitions

APERTURE JITTER (t_AJ) is the variation in aperture delay from sample-to-sample. Aperture jitter can be effectively considered as noise at the input.

CODE ERROR RATE (CER) is the probability of error and is defined as the probable number of word errors on the ADC output per unit of time divided by the number of words seen in that amount of time. A CER of 10^-18 corresponds to a statistical error in one word about every 31.7 years.

CLOCK DUTY CYCLE is the ratio of the time that the clock waveform is at a logic high to the total time of one clock period.

DIFFERENTIAL NON-LINEARITY (DNL) is the measure of the maximum deviation from the ideal step size of 1 LSB. It is measured at the relevant sample rate, f_CLK, with f_IN = 1MHz sine wave.

EFFECTIVE NUMBER OF BITS (ENOB, or EFFECTIVE BITS) is another method of specifying Signal-to-Noise and Distortion Ratio, or SINAD. ENOB is defined as (SINAD − 1.76) / 6.02 and states that the converter is equivalent to a perfect ADC of this many (ENOB) number of bits.

GAIN ERROR is the deviation from the ideal slope of the transfer function. It can be calculated from Offset and Full-Scale Errors. The Positive Gain Error is the Offset Error minus the Positive Full-Scale Error. The Negative Gain Error is the Negative Full-Scale Error minus the Offset Error. The Gain Error is the Negative Full-Scale Error minus the Positive Full-Scale Error; it is also equal to the Positive Gain Error plus the Negative Gain Error.

GAIN FLATNESS is the measure of the variation in gain over the specified bandwidth. For example, for the ADC12D1800RF, from D.C. to Fs/2 is to 900 MHz for the Non-DES Mode and from D.C. to Fs/2 is 1800 MHz for the DES Mode.

INTEGRAL NON-LINEARITY (INL) is a measure of worst case deviation of the ADC transfer function from an ideal straight line drawn through the ADC transfer function. The deviation of any given code from this straight line is measured from the center of that code value step. The best fit method is used.

INSERTION LOSS is the loss in power of a signal due to the insertion of a device, e.g. the ADC12D1800RF, expressed in dB.

INTERMODULATION DISTORTION (IMD) is a measure of the near-in 3rd order distortion products (2f₂ - f₁, 2f₁ - f₂) which occur when two tones which are close in frequency (f₁, f₂) are applied to the ADC input. It is measured from the input tones level to the higher of the two distortion products (dBc) or simply the level of the higher of the two distortion products (dBFS). The input tones are typically -7dBFS.

LSB (LEAST SIGNIFICANT BIT) is the bit that has the smallest value or weight of all bits. This value is

where V_FS is the differential full-scale amplitude V_{IN_FSR} as set by the FSR input and "N" is the ADC resolution in bits, which is 12 for the ADC12D1800RF.

LOW VOLTAGE DIFFERENTIAL SIGNALING (LVDS) DIFFERENTIAL OUTPUT VOLTAGE (V_ID and V_OD) is two times the absolute value of the difference between the V_D+ and V_D- signals; each signal measured with respect to Ground. V_OD peak is V_OD,P= (V_D+ - V_D-) and V_OD peak-to-peak is V_OD,P-P= 2*(V_D+ - V_D-); for this product, the V_OD is measured peak-to-peak.

Figure 9-1 LVDS Output Signal Levels

LVDS OUTPUT OFFSET VOLTAGE (V_OS) is the midpoint between the D+ and D- pins output voltage with respect to ground; i.e., [(V_D+) +( V_D-)]/2. See Figure 9-1.

MISSING CODES are those output codes that are skipped and will never appear at the ADC outputs. These codes cannot be reached with any input value.

MSB (MOST SIGNIFICANT BIT) is the bit that has the largest value or weight. Its value is one half of full scale.

NEGATIVE FULL-SCALE ERROR (NFSE) is a measure of how far the first code transition is from the ideal 1/2 LSB above a differential −V_IN/2. For the ADC12D1800RF the reference voltage is assumed to be ideal, so this error is a combination of full-scale error and reference voltage error.

NOISE FLOOR DENSITY is a measure of the power density of the noise floor, expressed in dBFS/Hz and dBm/Hz. '0 dBFS' is defined as the power of a sinusoid which precisely uses the full-scale range of the ADC.

NOISE POWER RATIO (NPR) is the ratio of the sum of the power outside the notched bins to the sum of the power in an equal number of bins inside the notch, expressed in dB.

OFFSET ERROR (V_OFF) is a measure of how far the mid-scale point is from the ideal zero voltage differential input.

Offset Error = Actual Input causing average of 8k samples to result in an average code of 2047.5.

OUTPUT DELAY (t_OD) is the time delay (in addition to Latency) after the rising edge of CLK+ before the data update is present at the output pins.

OVER-RANGE RECOVERY TIME is the time required after the differential input voltages goes from ±1.2V to 0V for the converter to recover and make a conversion with its rated accuracy.

PIPELINE DELAY (LATENCY) is the number of input clock cycles between initiation of conversion and when that data is presented to the output driver stage. The data lags the conversion by the Latency plus the t_OD.

POSITIVE FULL-SCALE ERROR (PFSE) is a measure of how far the last code transition is from the ideal 1-1/2 LSB below a differential +V_IN/2. For the ADC12D1800RF the reference voltage is assumed to be ideal, so this error is a combination of full-scale error and reference voltage error.

SIGNAL TO NOISE RATIO (SNR) is the ratio, expressed in dB, of the rms value of the fundamental for a single-tone to the rms value of the sum of all other spectral components below one-half the sampling frequency, not including harmonics or DC.

SIGNAL TO NOISE PLUS DISTORTION (S/(N+D) or SINAD) is the ratio, expressed in dB, of the rms value of the fundamental for a single-tone to the rms value of all of the other spectral components below half the input clock frequency, including harmonics but excluding DC.

SPURIOUS-FREE DYNAMIC RANGE (SFDR) is the difference, expressed in dB, between the rms values of the input signal at the output and the peak spurious signal, where a spurious signal is any signal present in the output spectrum that is not present at the input, excluding DC.

θ_JA is the thermal resistance between the junction to ambient.

θ_JC1 represents the thermal resistance between the die and the exposed metal area on the top of the HSBGA package.

θ_JC2 represents the thermal resistance between the die and the center group of balls on the bottom of the HSBGA package.

TOTAL HARMONIC DISTORTION (THD) is the ratio expressed in dB, of the rms total of the first nine harmonic levels at the output to the level of the fundamental at the output. THD is calculated as

Equation 2.

where

Second Harmonic Distortion (2nd Harm) is the difference, expressed in dB, between the RMS power in the input frequency seen at the output and the power in its 2nd harmonic level at the output.

Third Harmonic Distortion (3rd Harm) is the difference expressed in dB between the RMS power in the input frequency seen at the output and the power in its 3rd harmonic level at the output.

9.1.2 Third-Party Products Disclaimer

TI'S PUBLICATION OF INFORMATION REGARDING THIRD-PARTY PRODUCTS OR SERVICES DOES NOT CONSTITUTE AN ENDORSEMENT REGARDING THE SUITABILITY OF SUCH PRODUCTS OR SERVICES OR A WARRANTY, REPRESENTATION OR ENDORSEMENT OF SUCH PRODUCTS OR SERVICES, EITHER ALONE OR IN COMBINATION WITH ANY TI PRODUCT OR SERVICE.

9.2.1 Related Documentation

AN-1126 BGA (Ball Grid Array) , SNOA021

AN-2132 Synchronizing Multiple GSPS ADCs in a System: The AutoSync Feature, SNAA073