Download Prototype-Modifications-091412

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