Phototransistor fed to a transimpedance amplifier

Started by SilverLeo in sci.electronics.design6 years ago 45 replies

Hi all. I'm running through some test of a phototransistor signal conditioner, and I'm facing with wild noise issues. The conditioning is a...

Hi all. I'm running through some test of a phototransistor signal conditioner, and I'm facing with wild noise issues. The conditioning is a basic TIA stage: http://i.imgur.com/PcgglKZ.png Feedback resistor is 5K, feedback capacitor is 470pF, negative bias is -12V, and photocurrent is in the range 8uA-800uA. The bandwidth should be about 50kHz. Opamp is OPA2277UA. Problem is that phototrans...


OPA197 c-load stability

Started by Anonymous in sci.electronics.design8 months ago 22 replies

OPA197 is a great little opamp. 36 volts RRIO, 10 MHz, pA bias current, pretty good offset specs, 5 nV noise, EMI hardened. Like most opamps,...

OPA197 is a great little opamp. 36 volts RRIO, 10 MHz, pA bias current, pretty good offset specs, 5 nV noise, EMI hardened. Like most opamps, it is specified to be stable up to some capacitive load, 1 nF in this case. For bigger caps they show the usual R+C load stabilizing idea on the data sheet. That all ignores the Williams Effect, namely that a big enough cap will stabilize most anythin...


Any TopSpice Users Here?

Started by Jim Thompson in sci.electronics.design7 years ago 3 replies

Any TopSpice Users Here? I have an OpAmp model out there that runs fine on PSpice, LTspice, HSpice, etc., but balks on TopSpice. The error...

Any TopSpice Users Here? I have an OpAmp model out there that runs fine on PSpice, LTspice, HSpice, etc., but balks on TopSpice. The error report, from the TopSpice output file is: GSw_Sw3 N_22 -VB VALUE {((TANH(9.485/0.1*(V(SHUTDOWN, + GND)-0.5))+1)/2)*(V(N_22, -VB)/1)} 0*ERROR*: mismatched parentheses in above expression check result= -1 0*ERROR*: loading VALUE be...


5-volt tolerant CMOS

Started by John Larkin in sci.electronics.design9 years ago 38 replies

Lots of CMOS gates and such are tolerant of pin voltages above Vcc, typically rated for 7 volts max. Does anybody know what sort of input...

Lots of CMOS gates and such are tolerant of pin voltages above Vcc, typically rated for 7 volts max. Does anybody know what sort of input circuits are typically used? Does it behave like a zener? To ground? Some parts specify an allowed input curent in the pullup direction, some don't. I'm designing a really tiny board, and an opamp can potentially overdrive an analog mux, an FSA3157....


Quantization and sample/hold in spice

Started by Klaus Kragelund in sci.electronics.design5 years ago 19 replies

Hi I need to introduce and error in a signal, both quantization and sample/hold Sofar I have done it by placing an opamp based sample/hold...

Hi I need to introduce and error in a signal, both quantization and sample/hold Sofar I have done it by placing an opamp based sample/hold followed by a 8bit ADC (ADC8break) and a 8 bit DAC (DAC8break) But it doesn't feel right to use that much circuitry just to simulate an error in the system Anyone know if it can be done with ABM blocks? (sample and hold can be done with a zero order...


TIA-PD compensation, by eye

Started by George Herold in sci.electronics.design5 years ago 81 replies

Hi all, months ago I bought this screaming fet opamp (THS463) to gin up an old photodiode circuit. Put it in today, and the step response doesn't...

Hi all, months ago I bought this screaming fet opamp (THS463) to gin up an old photodiode circuit. Put it in today, and the step response doesn't look right. Here's 1 k ohm of gain w/ 10 pF across it. https://www.dropbox.com/s/ncswyuokm9hktb5/step-10pF.BMP?dl=0 A lot of wiggles, but the amplitude isn't big enough. Here's the uncompensated step. https://www.dropbox.com/s/rilf9gvmlwldaj...


Stepped sine wave

Started by George Herold in sci.electronics.design11 years ago 92 replies

This is a continuation of the 50kHz VCO thread I started last week. I tried the stepped sine wave idea as suggested by James A, and...

This is a continuation of the 50kHz VCO thread I started last week. I tried the stepped sine wave idea as suggested by James A, and Phil H. The circuit clocks a MC14017 at 10x(F) to make a stepped sine wave at frequency (F). The ten outputs from the 4017 are sent through appropriate resistors and into the summing junction of an opamp. Here=92s a =91scope shot of the stepped output overlaid...


ADA4522 opamp hangup

Started by John Larkin in sci.electronics.design4 years ago 47 replies

ADA4522 is an amazing amp. 55 volt supplies, low noise, 5 uV max offset, EMI hardened, pA bias current. But it has a hangup mode as a follower:...

ADA4522 is an amazing amp. 55 volt supplies, low noise, 5 uV max offset, EMI hardened, pA bias current. But it has a hangup mode as a follower: if the output goes to V+ the input back-to-back diodes keep both inputs above the legal common-mode range. Pity it's not RRIO. Similar amps from TI and Maxim seem to have the same issue. Here's one fix: https://www.dropbox.com/s/tdzs1ydi7quzbs7...


noise in LT Spice

Started by John Larkin in sci.electronics.design12 years ago 52 replies

I'm wanting to simulate noise in a TIA. It will use a discrete jfet at the input, then opamps. Check me out on this, please: I assume...

I'm wanting to simulate noise in a TIA. It will use a discrete jfet at the input, then opamps. Check me out on this, please: I assume the jfet models have built-in gate equivalent noise voltages and currents, somewhere in the model string. Also assume the the LTC opamp models include noise params. Ditto Johnson noise in all resistors. The LT Spice help pdf file says that.....


poor op-amp settling time

Started by Winfield Hill in sci.electronics.design3 years ago 17 replies

I selected a Maxim MAX4239 opamp for a low-power design project, for its 2.5uV offset, its Iq = 0.6mA, and for G> 10, its 6.5MHz GBW. For...

I selected a Maxim MAX4239 opamp for a low-power design project, for its 2.5uV offset, its Iq = 0.6mA, and for G> 10, its 6.5MHz GBW. For G=10, that's a 650kHz -3dB bandwidth. Slew 1.6V/us. Response, t = 1/pi 650kHz = 0.5us. But the datasheet's 0.1% settling time spec is 500us, 1000x times slower! Makes little sense. Sad. Dunno whether to believe a very poor datasheet number.


Phil H MMIC as TIA

Started by Anonymous in sci.electronics.design3 years ago 1 reply

Phil, Have you ever considered using a darlington-type MMIC, like a Mini-Circuits part, as a fast photodiode TIA? Apart from scant specs, and...

Phil, Have you ever considered using a darlington-type MMIC, like a Mini-Circuits part, as a fast photodiode TIA? Apart from scant specs, and no Spice model, and ghastly DC behavior, it ought to work. They are cheap, stable, and super fast. Conventional opamp-type TIAs run out of speed low, and commercial ROSA-type things are mostly useless for DC-coupled applications. As you note in yo...


Unequivalent Input Impedance in Differential OpAmp Circuit

Started by Rick C in sci.electronics.design3 years ago 21 replies

I have an existing design that uses a single op amp stage with differential inputs and AC coupling caps on the inputs. The circuit acts as a 5:1...

I have an existing design that uses a single op amp stage with differential inputs and AC coupling caps on the inputs. The circuit acts as a 5:1 divider so the two input resistors are 51 kohms and the feedback resistor as well as the ground resistor in the non-inverting input leg are 10 kohms. The input caps are sized to maintain a good low frequency response. Many years ago I


strange second-order active lowpass filter

Started by Anonymous in sci.electronics.design1 year ago 8 replies

This is a new-to-me lowpass topology, roughly 2nd order Bessel. The final RC stomps opamp high-frequency noise. Version 4 SHEET 1 880...

This is a new-to-me lowpass topology, roughly 2nd order Bessel. The final RC stomps opamp high-frequency noise. Version 4 SHEET 1 880 680 WIRE 96 32 48 32 WIRE 656 32 160 32 WIRE 368 112 336 112 WIRE 336 144 336 112 WIRE -160 160 -224 160 WIRE -96 160 -160 160 WIRE 48 160 48 32 WIRE 48 160 -16 160 WIRE 304 160 48 160 WIRE 448 176 368 176 WIRE 480 176 448 176 WIRE 512 176 480 176...


boosted opamp

Started by Anonymous in sci.electronics.design3 years ago 8 replies

This might work: Version 4 SHEET 1 1080 680 WIRE 64 -48 -144 -48 WIRE 400 -48 64 -48 WIRE -144 -16 -144 -48 WIRE -416 0 -512 0 WIRE...

This might work: Version 4 SHEET 1 1080 680 WIRE 64 -48 -144 -48 WIRE 400 -48 64 -48 WIRE -144 -16 -144 -48 WIRE -416 0 -512 0 WIRE -288 0 -336 0 WIRE 400 0 400 -48 WIRE -512 48 -512 0 WIRE 336 48 304 48 WIRE -144 96 -144 64 WIRE 64 96 64 -48 WIRE 32 112 -32 112 WIRE 144 128 96 128 WIRE 176 128 144 128 WIRE 256 128 240 128 WIRE 304 128 304 48 WIRE 304 128 256 128 WIRE 400 12...