spopa2
Bioengineer
- May 4, 2011
- 9
I am building a wien bridge oscillator using an LMV751 opa with an output frequency of 20khz.
The breadboard version of the circuit above works perfectly, the output voltage is around 400mV pp at 20kHz. The breadboard version uses the SMD version of the LMV751 on a breakout board, and 1N4148 diodes.
The SMD version of the circuit is constructed exactly the same, with the only difference that it uses BAS16 diodes. However, a version was tested where 1N4148 diodes were soldered to the board instead.
Both circuits are completely isolated from any other components, and tested using the same power supply, which outputs 3.1V for Vcc, 1.52V Vcc/2.
The issue is that the SMD version has a much higher amplitude of 2Vpp, although it oscillates at extacly 20kHz also. The circuit was tested with two LMV751 chips incase it was a chip defect.
As you can see in the pictures, the breadboard version takes much longer to start oscillating than the SMD version.
Breadboard version at startup
PCB version at startup (NOTE: frequency is the same as the previous image, it appears lower due to aliasing on the scope screen) Also, the circuits were analyzed again using exactly the same input voltage and the results were the same, I just didn't take a picture.
The circuits were build from scratch again and checked over multiple times for any error or difference between them. All passive components (0.1% tolerance ) are confirmed to be exactly the same.
I am completely stumped and have know idea what would be causing such behavior. Any suggestions are greatly appreciated.
Thank you!!
Sorin

The breadboard version of the circuit above works perfectly, the output voltage is around 400mV pp at 20kHz. The breadboard version uses the SMD version of the LMV751 on a breakout board, and 1N4148 diodes.
The SMD version of the circuit is constructed exactly the same, with the only difference that it uses BAS16 diodes. However, a version was tested where 1N4148 diodes were soldered to the board instead.
Both circuits are completely isolated from any other components, and tested using the same power supply, which outputs 3.1V for Vcc, 1.52V Vcc/2.
The issue is that the SMD version has a much higher amplitude of 2Vpp, although it oscillates at extacly 20kHz also. The circuit was tested with two LMV751 chips incase it was a chip defect.
As you can see in the pictures, the breadboard version takes much longer to start oscillating than the SMD version.

Breadboard version at startup

PCB version at startup (NOTE: frequency is the same as the previous image, it appears lower due to aliasing on the scope screen) Also, the circuits were analyzed again using exactly the same input voltage and the results were the same, I just didn't take a picture.
The circuits were build from scratch again and checked over multiple times for any error or difference between them. All passive components (0.1% tolerance ) are confirmed to be exactly the same.
I am completely stumped and have know idea what would be causing such behavior. Any suggestions are greatly appreciated.
Thank you!!
Sorin