PCB layout check.

Hello Parag,

Please specify the TI devices used in this design.  A schematic would also be helpful.

Regards,

~Leonard 

Hi leonard 

Can I have your mail id? I will send the complete schematic with component details there. 

sent via Private message

Hello Parag,

We would need to see the solder mask so that it can be shown where the OPA37 and OPA2111 are located on the board.

Regards, Thomas

Precision Amplifiers Applications Engineering

Hello sir,

I attached the solder mask file in the attachment. Kindly see and suggest any correction if any. In this file U3, U4, U17 and U19 are the OA2111 and rest are OPA37.

Hi Thomas Sir,

I Have provided the required details in the post. I have prepared the prototype of that PCB but it is not working. If you can help me to fix the problem then it would be a great help. I can share more information like schematic and TINA software file if you required.

Best regards Parag

Hello Parag,

I am looking over your PC board layout. This is not a fast process because I have to visually compare the board and your schematic. If I find something that doesn't look correct I will let you know.

When your mention the prototype is not working, what is it doing/or not doing?

Regards, Thomas

Precision Amplifiers Applications Engineering

Hello Parag,

We have been reviewing your PC board design. There may be problems with the bottom side ground plane. It looks like there is at least one interruption in the ground plane that separates and isolates regions of the plane from each other. Also, the ground plane does get necked down to some very narrow passages that may not prevent operation, but could affect performance.

Does your PC board layout software do design rule check (DRC)? If so, it should find layout violations - but not schematic errors.

Regards, Thomas

Precision Amplifiers Applications Engineering

Hello sir,

I have traced the fault in the PCB prototype and correct it using the jumpers to check its operation. While doing this I found that some unusual errors are coming.

1. In the transmitting and receiving switching stage (TR), I use WO4 bridge rectifier in the D2 place but the signal is totally lost there. While the same circuit design is correctly working in TINA simulation.

2. At the DC blocking capacitor (C5) and series resistance (R42) I don't know why the amplitude of my signal is suddenly decreasing. Similarly happens with the R1 resistor.  If you can help to find the right choice (type and value) of those capacitors and resistor, I will be highly thankful.

Best Regards

Parag

Hello Parag,

The two-stage OPA2111 dual amplifier band-pass (DABP) filters have a center frequency of 2.26 kHz, a very narrow passband, and steep skirts. I wasn't sure which side of R42 and R1 you were making the measurement, but in either case because of the filter characteristics the amplitude will be down substantially if you are not right on the band-pass filter center frequency. As you move off the center frequency the amplitude will drop very quickly. You can see this in the simulation results shown below.

Regards, Thomas

Precision Amplifiers Applications Engineering

Hello sir,

Actually, I designed this circuit for 2.25KHz central frequency. I may have done some calculation wrong definitely. But instead of using the source of 2.26KHz, the results are not improving. I am getting super confused now, as per my calculation my bandwidth must be 50Hz and central frequency at 2.25Khz. I got two questions on this design.

1.  As per my knowledge, the capacitor and resistors after the OPA27 amplifier are for blocking the DC content and limiting the excess current. What is the maths behind choosing the correct value for these components? And why the shape of my results distorted after sorting these?

2.  Where my calculation has gone wrong in making the DABP. 

Hello Parag,

Regarding your questions:

1.  As per my knowledge, the capacitor and resistors after the OPA27 amplifier are for blocking the DC content and limiting the excess current. What is the maths behind choosing the correct value for these components? And why the shape of my results distorted after sorting these?

The high-pass corner frequency resulting from the pole created by R1 (45 kΩ) and C5 (100 nF) in my TINA schematic is simply fp = 1/(2πR₁C₅). That equates to a pole in the response at 35 Hz, which is exactly the frequency that is obtained from a TINA simulation.

2.  Where my calculation has gone wrong in making the DABP. 

 I didn't see your calculations, but let's assume you didn't make an error because your filter comes very close to having the calculated center frequency (fc).

Actually, if the center frequency fC is 2.26 kHz and you designed for 2.25 kHz you are not far off. The most common reason for an active filter having a response that is somewhat different than designed is component tolerances of the resistors and capacitors; especially capacitors. It is often easy to obtain 1 % tolerance resistors, but not so for capacitors. Often, without giving it much thought designers incorporate capacitors having a 5 % tolerance in their filter designs.

I recommend using the lowest tolerance resistors and capacitors you can practically use; +/-0.1 % tolerance resistors, and +/-2 % capacitors - preferably C0G. Selecting like value resistors and capacitors off the same reel, one next to the other, often results in close matching between them.

The second most common for the filter response being different than expected is the Op amp selected has too low of Gain Bandwidth (GBW) to support the required response. The OPA2111 2 MHz GBW should be sufficient to support a DABP filter having a 2.25 kHz BW. Therefore, I suspect component tolerances are causing the error.

Regards, Thomas

Precision Amplifiers Applications Engineering