In modern radio receivers, the sampling rate of the ADC1. analog-to-digital converterCircuit that converts an analog input signal into digital values.2. automated data collectionSystem or method for collecting, storing, exchanging or analyzing data.3. automatic defect classificationMeasurement or inspection concept for tracking defects and process variations in manufacturing. and the complexity of the anti-alias filter in front of it are tightly linked. Sampling closer to the Nyquist limit narrows the transition band that the analog filter must cover, which quickly drives up filter order. Sampling faster relaxes that filter, but in a conventional chain it also increases converter cost and the amount of data the FPGAfield-programmable gate arrayReconfigurable logic device whose internal circuits can be programmed after manufacturing. or ASICapplication-specific integrated circuitIntegrated circuit customized for a specific task must handle.
The article compares three receiver architectures built around a 14-bit dual-channel ADC1. analog-to-digital converterCircuit that converts an analog input signal into digital values.2. automated data collectionSystem or method for collecting, storing, exchanging or analyzing data.3. automatic defect classificationMeasurement or inspection concept for tracking defects and process variations in manufacturing. with an embedded DSP1. differential signal processingSignal processing based on differences between two signals, often rejecting common interference.2. digital signal processing block from Silanna’s SD1148 family. That DSP1. differential signal processingSignal processing based on differences between two signals, often rejecting common interference.2. digital signal processing block adds decimation, digital downconversion, and IQ mismatch correction on chip, shifting part of the front-end processing away from the FPGAfield-programmable gate arrayReconfigurable logic device whose internal circuits can be programmed after manufacturing.. The device family supports sample rates from 40 to 250 MS1. mass spectrometryAnalytical measurement method that derives sample properties from a characteristic spectrum.2. mass spectrometerInstrument or sensing element for measuring and analyzing physical or chemical quantities.3. mass spectroscopyAnalytical measurement method that derives sample properties from a characteristic spectrum./s.
The first example is a direct conversion receiver for a 26 MHzmegahertzFrequency unit equal to one million cycles per second.-wide band centered at 915 MHzmegahertzFrequency unit equal to one million cycles per second.. After quadrature downconversion, the I and Q signals extend from 0 to 13 MHzmegahertzFrequency unit equal to one million cycles per second.. The ADC1. analog-to-digital converterCircuit that converts an analog input signal into digital values.2. automated data collectionSystem or method for collecting, storing, exchanging or analyzing data.3. automatic defect classificationMeasurement or inspection concept for tracking defects and process variations in manufacturing. runs at 65 MS1. mass spectrometryAnalytical measurement method that derives sample properties from a characteristic spectrum.2. mass spectrometerInstrument or sensing element for measuring and analyzing physical or chemical quantities.3. mass spectroscopyAnalytical measurement method that derives sample properties from a characteristic spectrum./s, leaving a wide anti-alias transition band. A decimator set to 2 reduces the output rate to 32.5 MS1. mass spectrometryAnalytical measurement method that derives sample properties from a characteristic spectrum.2. mass spectrometerInstrument or sensing element for measuring and analyzing physical or chemical quantities.3. mass spectroscopyAnalytical measurement method that derives sample properties from a characteristic spectrum./s, while the on-chip FIR filter provides the needed low-pass response and the DSP1. differential signal processingSignal processing based on differences between two signals, often rejecting common interference.2. digital signal processing block corrects DCdirect currentElectric current that flows in one direction. offset, IQ gain mismatch, and IQ phase error.
The second configuration keeps the same RF1. radio frequencyHigh-frequency electromagnetic oscillations used, for example, to excite plasmas.2. resonance frequencyQuantity describing a signal’s frequency, bandwidth, spectral behavior or transmission rate. and analog front end, but uses the built-in DDC for digital channel selection within the digitized band. The 26 MHzmegahertzFrequency unit equal to one million cycles per second. span is divided into four 6.5 MHzmegahertzFrequency unit equal to one million cycles per second. channels, and the NCO shifts the selected channel to 0 Hz before decimation by 4. The output rate drops to 16.25 MS1. mass spectrometryAnalytical measurement method that derives sample properties from a characteristic spectrum.2. mass spectrometerInstrument or sensing element for measuring and analyzing physical or chemical quantities.3. mass spectroscopyAnalytical measurement method that derives sample properties from a characteristic spectrum./s. The text also notes that lowering the ADC1. analog-to-digital converterCircuit that converts an analog input signal into digital values.2. automated data collectionSystem or method for collecting, storing, exchanging or analyzing data.3. automatic defect classificationMeasurement or inspection concept for tracking defects and process variations in manufacturing. rate into the 50 to 55 MS1. mass spectrometryAnalytical measurement method that derives sample properties from a characteristic spectrum.2. mass spectrometerInstrument or sensing element for measuring and analyzing physical or chemical quantities.3. mass spectroscopyAnalytical measurement method that derives sample properties from a characteristic spectrum./s range can still keep the anti-alias filter manageable while reducing downstream data volume.
The third design uses IF1. interfaceInterface or communications concept for transmitting data between devices and systems.2. intermediate focus sampling for a 40 MHzmegahertzFrequency unit equal to one million cycles per second. RF1. radio frequencyHigh-frequency electromagnetic oscillations used, for example, to excite plasmas.2. resonance frequencyQuantity describing a signal’s frequency, bandwidth, spectral behavior or transmission rate. signal in the 2.4 GHz ISMinductor super magnetron band. Here the signal is first converted to a 150 MHzmegahertzFrequency unit equal to one million cycles per second. IF1. interfaceInterface or communications concept for transmitting data between devices and systems.2. intermediate focus and then digitized at 200 MS1. mass spectrometryAnalytical measurement method that derives sample properties from a characteristic spectrum.2. mass spectrometerInstrument or sensing element for measuring and analyzing physical or chemical quantities.3. mass spectroscopyAnalytical measurement method that derives sample properties from a characteristic spectrum./s, placing the IF1. interfaceInterface or communications concept for transmitting data between devices and systems.2. intermediate focus in the second Nyquist zone. That requires band-pass anti-alias filtering with a passband from 130 MHzmegahertzFrequency unit equal to one million cycles per second. to 170 MHzmegahertzFrequency unit equal to one million cycles per second.. The approach avoids direct-conversion issues around DCdirect currentElectric current that flows in one direction. and IQ matching, but it pushes image rejection and sampling-clock jitter requirements higher. In this case, the ADC1. analog-to-digital converterCircuit that converts an analog input signal into digital values.2. automated data collectionSystem or method for collecting, storing, exchanging or analyzing data.3. automatic defect classificationMeasurement or inspection concept for tracking defects and process variations in manufacturing.’s digital mixer and decimation functions complete the second conversion stage after sampling.