Hello,
I need a bit of help with a bandpass filter circuit. I used Texas Instruments software to design a 4th order bandpass filter
using the THS4032 op amp chip.
I made a prototype PCB that lets me switch jumpers to run in dual supply mode or single supply mode. I have some
applications for both so I wanted to try them both out. I've attached a schematic for the TI design and the actual circuit
I designed.
I designed a PCB and assembled the circuit and tested in dual supply mode and it works perfectly. When I try to run in
single supply mode I cannot bias the op amp input to 6V. The power source for single supply is +12V. For dual supply
mode I set all jumpers between pins 2 and 3. For single supply I set all jumpers between pins 1 and 2.
In single supply mode I measure 12.13 volts at the right side of R15, but 8.60 volts across it. I measure 3.48 volts across
R14 and about 3.5 volts with respect to ground right in between R14 and R15 (I want this to be 6volts). If I remove the
jumper from JP5 I see exactly 6 volts at pin 1 of JP5 and 6 volts across R14 and R15 as I would expect.
I see the same type of behavior with the bias point between resistor R26 and R27.
Does anyone have an idea what could be wrong? In a different version circuit for a high pass filter I use the same
technique for biasing and it works perfectly in single or dual supply mode. I've double checked all my PCB design and
components and they check out fine. I've built two of these circuits and they both behave exactly the same.
I just wanted to know if anyone sees anything I'm doing wrong from the design itself.
I need a bit of help with a bandpass filter circuit. I used Texas Instruments software to design a 4th order bandpass filter
using the THS4032 op amp chip.
I made a prototype PCB that lets me switch jumpers to run in dual supply mode or single supply mode. I have some
applications for both so I wanted to try them both out. I've attached a schematic for the TI design and the actual circuit
I designed.
I designed a PCB and assembled the circuit and tested in dual supply mode and it works perfectly. When I try to run in
single supply mode I cannot bias the op amp input to 6V. The power source for single supply is +12V. For dual supply
mode I set all jumpers between pins 2 and 3. For single supply I set all jumpers between pins 1 and 2.
In single supply mode I measure 12.13 volts at the right side of R15, but 8.60 volts across it. I measure 3.48 volts across
R14 and about 3.5 volts with respect to ground right in between R14 and R15 (I want this to be 6volts). If I remove the
jumper from JP5 I see exactly 6 volts at pin 1 of JP5 and 6 volts across R14 and R15 as I would expect.
I see the same type of behavior with the bias point between resistor R26 and R27.
Does anyone have an idea what could be wrong? In a different version circuit for a high pass filter I use the same
technique for biasing and it works perfectly in single or dual supply mode. I've double checked all my PCB design and
components and they check out fine. I've built two of these circuits and they both behave exactly the same.
I just wanted to know if anyone sees anything I'm doing wrong from the design itself.
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