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Transcript
Amplitude Feedback Subcircuit Schematic Modifications Reference Level Shifter Envelope Detectors Feedback Log Amps Error Calculator Attenuator Level Shifter Without level shifters, envelope detector output does not overlap with full input range of log amp. Level shifters increase correction range. Candidate Topologies for Level Shifters • Op-amp level shifter + Accurate and easily adjusted – Limited bandwidth due to wires splicing it onto PCB • AC coupling + Simple, easiest modification – Blocks low frequency components of signal • Diode level shifting circuit + Simple, easy modification – Some distortion due to voltage drop across diode • Tested each topology on breakout boards and on PCB Diode level shifter performed best on system board Phase Detector Output Signals for Single Tone Inputs 500 MHz • Distinct logic “hi” and “low” levels • Well defined square wave output • Accurate phase error measurements 2 GHz • Indeterminate logic “hi” and “low” levels • Not a well defined square wave output • Invalid phase error measurements Phase Detector & Error Measurement Subcircuit Schematic Phase Shifter Error Calculator Proposed modifications: •Prescaler (frequency divider) • Reduce frequency by ½ or ¼ • Tested successfully 1-tone Phase Detector •Comparator • Clean up inputs (fast rising edge) • Testing evaluation boards •Both subcircuits are “add-ons” Phase FB Vref Comparator Attenuator Prescaler Phase Ref Comparator Vref Candidate Prescalers & Dividers On Semi Prescalers & Dividers* Part # Description Propagation Delay (pS) Not specified Rise & Fall Times (pS) Not specified MC12095 NB7L32M 2.5 GHz prescaler, 2 or 4 2.5V, CML, 2 200 30 MC10EP32 3.3V, ECL, 2 350 120 MC10EL33 5V, ECL, 4 650 225 * Initially limiting candidates to On Semi components to ensure compatibility w/ phase detector Test Status: the MC12095 was tested successfully at 2.14 GHz Circuits for Sharp Input Edges • Schmitt Trigger Inverters – Commercially available • SN74AUC1G04 VH = 1.2V, 0.8 nS propagation delay • NLX3G14 VH = 1V, 4 nS propagation delay – Non-Commercially available • VH=0.42V, 170 pS switching speed • Comparators – Analog Devices ADCMP573, propagation delay 150 pS – On Semi MC10E1651, propagation delay 775 pS – Linear Technology LTC5564, typical response time 7 nS ADCMP572 Evaluation Board Measurement Outputs Input f = 5 MHz Typical rise and fall times for ADCMP57X are specified as 35 pS