Hi champs,
My customer evaluated OPA4170 and OPA4171 with attached circutry.
As shown in attached file, when OPA4710 was applied, output sinsoidale waveform shows distortion, but OPA4171 works better.
Could you explain from design point of view, waht is major difference between OPA4170 and OPA4171?
Best regards,
Hi Nobuo,
Both OPA4170 and OPA4171 are rail to rail CMOS amplifiers.
The key differences between them are summarized below:
|
OPA 4170 |
OPA 4171 |
|
GBW = 1.2 MHz |
GBW = 3 MHz |
|
Slew Rate = 0.4 V/us |
Slew Rate = 1.5 V/us |
|
Quiescent Current = 0.1 mA |
Quiescent Current = 0.475 mA |
|
Voltage Noise @ 1kHz = 19 nV/rtHz |
Voltage Noise @ 1kHz = 14 nV/rtHz |
Highlighted in yellow might be the root cause to distortion you're experiencing .
From the above waveform:
# Of Divisions per cycle = 2.5
@ 20 us/div ; T = 50 us per cycle
Frequency = 1/T = 20 kHz
For OPA 4170: V_Out_Peak= (Slew Rate)/2πf= (0.4 V/us)/(2*π*20kHz)=3.183 V_pk
For OPA 4171: V_Out_Peak= (Slew Rate)/2πf= (1.5 V/us)/(2*π*20kHz)=11.937 V_pk
In your application, if you’re nearing 3 Vpk_output with OPA 4170 you may see distortion induced due to slew rate.
Can you also please check that your output current is below the specification for both configurations? A quick way to check if this caused distortion is to increase the load impedance 10X to see if that fixes the distortion.
Note: Since we are comparing similar amplifiers. General rule of thumb is Increase in Iq, Bandwidth, Slew rate; Decreases distortion and Noise.
Best Regards,
Bala Ravi
