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AD9022 Arkusz danych(PDF) 7 Page - Analog Devices |
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AD9022 Arkusz danych(HTML) 7 Page - Analog Devices |
7 / 12 page AD9022 –7– REV. A 0 120 10.0 100 0.0 60 80 40 20 8.0 6.0 4.0 2.0 FREQUENCY – MHz AIN1 = 8.9MHz AIN2 = 9.8MHz AIN1 = 7.0dBFS AIN2 = 7.0dBFS SFDR = 80.62dBFS Analog input signals are immediately attenuated through a resis- tor divider and applied directly to the sampling bridge of the track-and-hold (T/H). The T/H holds whatever analog value is present when the unit is strobed with an ENCODE command. The conversion process begins on the rising edge of this pulse, which should conform to the minimum and maximum pulse width requirements shown in the specifications. Operation be- low the recommended encode rate (4 Msps) may result in ex- cessive droop in the internal T/H devices–leading to large dc and ac errors. The held analog value of the first track-and-hold is applied to a 5-bit flash converter and a second T/H. The 5-bit flash con- verter resolves the most significant bits (MSBs) of the held ana- log voltage. These 5 bits are reconstructed via a 5-bit DAC and subtracted from the original T/H output signal to form a residue signal. A second T/H holds the amplified residue signal while it is en- coded with a second 5-bit flash ADC. Again the 5 bits are re- constructed and subtracted from the second T/H output to form a residue signal. This residue is amplified and encoded with a 4- bit flash ADC to provide the 3 least significant bits (LSBs) of the digital output and one bit of error correction. Digital Error Correction logic aligns the data from the three flash converters and presents the result as a 12-bit parallel digi- tal word. The output stage of the AD9022 is TTL. Output data may be strobed on the rising edge of the ENCODE command. AD9022 IN RECEIVER APPLICATIONS Advances in semiconductor processes have resulted in low cost digital signal processing (DSP) and analog signal processing which can help create cost effective alternative receiver designs. Today, an all-digital receiver allows tuning, demodulation, and detection of receiver signals in the digital domain. By digitizing IF signals directly and utilizing digital techniques, it becomes possible to make significant improvements in receiver design. For high frequency IFs, the ADC is the key to the receiver’s per- formance. Unfortunately, the specifications frequently used by receiver designers and analog-to-digital (ADC) manufacturers are often very different. Noise Figure and Intercept Point are common measures of noise and linearity in analog RF system design. ADCs are more frequently specified in terms of SNR and harmonic distortion. Noise Noise figure (NF) is a measure of receiver sensitivity and is de- fined as the degradation of signal-to-noise ratio (SNR) as a sig- nal passes through a device. In equation form: NF = SNR (in) – SNR (out) Noise figure is a bandwidth invariant parameter for reasonably narrow bandwidths in most devices. The system noise figure for a combination of amplifiers and mixers, for instance, can be analyzed without regard to the information bandwidth. Thermal noise contribution from the ADC behaves in a similar fashion; however, the spectral density of quantization noise is a function of the sample rate. In addition, the spectral density of the quantization noise is flat only in an ADC with perfect linear- ity, i.e., perfect 1 LSB step sizes. To analyze the system noise performance, ADC noise figure is calculated by normalizing the SNR of the ADC output to a 1 Hz bandwidth. This result is given by: SNR (/Hz) = SNR + 10 log10 (Fs/2) where Fs is the sample rate. 0 –100 –70 –90 –80 –40 –60 –50 –30 –20 –10 10 0 FREQUENCY – MHz AIN = 1.2MHz AIN = –1.0dBFS SNR = 66.7dB THD = 77.51dB SFDR = 79.49dBFS THEORY OF OPERATION Refer to the block diagram. The AD9022 employs a three-pass subranging architecture and digital error correction. This combination of design techniques ensures 12-bit accuracy at relatively low power. 0 –100 –70 –90 –80 –40 –60 –50 –30 –20 –10 10 0 FREQUENCY – MHz AIN = 9.6MHz AIN = –1.0dBFS SNR = 66.05dB THD = 74.28dB SFDR = 75.32dBFS Figure 8. FFT Plot Figure 9. FFT Plot Figure 10. Two Tone FFT OBSOLETE |
Podobny numer części - AD9022_15 |
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Podobny opis - AD9022_15 |
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