文稿ni官方培训labview rf lesson

1、Lesson 6Digitizers and Arbitrary Waveform Generators (AWGs)DC Offsets and Peak-to-Peak VoltagesMaximizing Dynamic RangeImpedance ConsiderationsSingle-to-Differential Signal ConversionEffective Number of Bits (ENOB)Block Diagram of Digital Upconversion (DUC) and Digital Downconversion (DDC)Resolution

2、 Bandwidth (RBW)A. DC Offsets and Peak-to-Peak VoltagesRFDC of little or no concern, decoupledMixed SignalExtremely importantThese signal components are measuredDC Offset Effect for Baseband and RFBaseband / Mixed SignalRFIdeal0.1 VDCOffsetB. Maximizing Dynamic RangeTo minimize sampling error and ma

3、ximize dynamic range, choose the smallest least significant bit (LSB) possible according to the following relationship:Maximizing Dynamic Range Example Digitizer has 2 V, 1 V, 500 mV, 250 mV (12 bits)Signal has 200 mV DC offset, 230 mV peak-to-peakCould use 500 mV range Better to use 250 mV rangeSte

4、p size (250 mV range) = 122 VStep size (500 mV range) = 244 VBenefit: Twice the accuracyC. Impedance ConsiderationsTypical zero (ZIF) receivers have different input/output impedances.How do we measure gain?For large values of R , V is comparatively unaffected.Better to compare input/output voltages

5、than input/output power.D. Single-to-Differential Signal ConversionE. Effective Number of Bits (ENOB)RF engineers are interested in noise figure and noise floor.Mixed-signal engineers are interested in dynamic range and effective number of bits.Possible for 14-bit digitizer to have higher or lower E

6、NOB.ENOB and Noise FloorExample Calculation:10.4 ENOB digitizer using 10 kHz BW, 1 Vpp, 50 (full scale)SNR = 64.7 dB Peak signal = 3.9 dBm, thus noise floor = 60.5 dBm /10 kHz, or noise floor = 60.5 10*log(BW) = 100.5 dBm/HzF. Block Diagram of Digital Upconversion (DUC) and Digital Downconversion (D

7、DC)Interpolate/decimate baseband data to/from a higher sample rate Lowpass filter the high sample rate data Frequency translate the baseband data (mix with carrier) Combine/demultiplex baseband /IF dataG. Resolution Bandwidth (RBW) Effects of lowering resolution bandwidth:Increases frequency resolut

8、ion (# of spectral lines)Lowers noise floorIncreases dynamic range narrowband signals only Increases acquisition time.HzSummaryDC offset has powerful effects of mixed-signal systems but little effect on RF systems.To minimize sampling error and maximize dynamic range, choose the smallest LSB possible.As the RBW is lowered, the resolu