Other Parts Discussed in Thread: BUF602, , TINA-TI
Hi,
I would like to build fast peak detector. It should be analog circiut.
I decided to try with OPA615 and BUF602 IC.
The signal to measure: PPM, 4MHz, 10ns pulse amplitude from 10 mV to 5V. The very short pulse time is problem in this design.
I don't need ultra fast and precision detector. Error around few % and reaction time in ms is acceptable to me.
I think that OTA and fast comparator in OPA615 is good solution.
I built the circuit from datasheet on two sided PCB with good rules of design (all SMD, well grounded capacitors etc.)
In first version I used DB3X314 diodes (1ns, 300nA reverse current, 1pf) and 22pF capacitors.
Iq of OPA615=13mA
Supply +/-5V.
Hold control pin not conected.
Below my results with 10ns pulses with 250ns repetition:
BLUE - INPUT SIGNAL
MAGENTA - POSITIVE OUTPUT SIGNAL FROM DETECTOR
-100mVpp
-300mVpp
-500mV
-1Vpp
-1Vpp but 1MHz and 500ns pulse to compare
THEN I CHANGED CAPACITORS TO 1nF
I CHANGED DIODES TO BAS16 AND 22pf CAP
I CHANGED CAPACITORS TO 1nF (BAS16 diodes)
1) What my detector lowers amplitude - capacitor is not charged to peak value?
2)It is possible to built 10ns peak detector with OPA615?
3)How i can built analog fast peak detector for 10ns pulses if OPA615 is not suitable? Wchich IC (OPAMP/COMPARATOR) i must use?
I need to detect low amplitude pulses - from 10mV.
I conluded that:
-capacitor value is important - small cap. is fast charged and too fast discharged.
-diodes has parasitic capacity and forward current which discharge my detector capacitor.
- I had different results witch different diodes
- detector for pulses above 100ns works good.
Where is the problem? Damage OTA? Diode? Capacitor? Bad design? OPA too slow?
Other solutions:
www.edn.com/.../High-speed-peak-detector-uses-ECL-comparator
