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Part Number: TL026
I would like to be able to teach you the following points regarding the TL026C.
The circuit is designed using TL026C as shown in Figure 1.
・ Input: Connect a signal of amplitude 40mVp-p to IN + with a capacitor, and terminate with a resistor. IN- connects to GND.
・ Output: Control AGC terminal so that the signal is output at 1.2 Vp-p from OUT +. OUT- is open.
・ Power supply: Connect Vcc + to 4.5V and Vcc- to -4.5V.
・ Operating temperature: 0 ° C to 85 ° C
In this circuit, the voltage at the AGC pin is changed in a 25 ° C environment, and the gain of the TL026C is measured from the output of the OUT + pin, as shown in the graph in Figure 2.
① Due to the relationship between AGC voltage and Gain, the graph of the specification document (Figure 3) reads that Gain up to 85 times can be obtained at 25 ° C environment, but in measurement Gain(Figure 2) is obtained only up to 35 times. (Maximum Gain 70 times, even considering differential) Please explain the reason why Gain can not be obtained according to the specifications.
② From the relationship between the “AVD Large-signal differential voltage amplification (MIN 55 to MAX 115 [V / V])] in the specification sheet and the graph in Figure 2, the TL026C output Gain 30 times of our circuit is Are there any problems as a condition for using TL026C? If you have a problem, please tell us "What concerns do you have?" And "How much gain should I use?"
③ In our circuit, when the output gain of the TL026C is designed to be 10 times, the change in gain at a frequency of about 10 Hz and noise of a frequency of 50 kHz appear in the output signal of the TL026C.
Can you give me some advice to remove these noise components? (Figure 4)
④ In our circuit, when the output gain of the TL026C is designed to be 10, 25 or 30 times, undershoot / overshoot appears in the output signal as the gain becomes higher.
The undershoot / overshoot becomes larger as the gain is higher. Can you give me some advice for removing these undershoots /overshoots?
⑤ What is the proper range of use for the TL026C REF OUT pin output current?
1) The gain at OUT+ and OUT- doesn't have to be balanced. I have a memory that is is it not balanced, but I can not locate this data. I will need to test this early next week. Most of the examples in data sheet have a load on OUT-; this may or may not be required.
2) The minimum gain at temperature is 55V/V, so 30V/V on one output may not always be possible. Using a difference amplifier on OUT+ and OUT- is best to get most gain from TL026 and to remove the output common mode offset.
3) Does the AGC signal, IN+ voltage, or anything else in the system have a 10 Hz component?
4) I would not expect overshoot, do you have a waveform demonstrating this effect?
5) Per data sheet tables: Vref Voltage at REF OUT Iref = – 1 mA to 100 mA has Vref 1.3 to 1.5 V
Regards,Ronald MichallickLinear Applications
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In reply to Ron Michallick:
There is also the LM13700 that is useful for variable gain. It has two channels and single ended outputs. The bandwidth of LM13700 is less, but I expect that this not an issue for your application signal.
I checked TL026 in lab today.
First is maximum gain of Vref-200mV (single ended no load, VCC +/-4.5V)
In the middle, OUT+ gain is 42.5 and OUT- is 32.6V/V
The most noteworthy aspect is that clipping occurs at -25mV and +35mV input. You may need to attenuate your input signal a little or accept clipping.
Here is difference output. Gain is 76.1
Here is diff minimum gain (single end minimum gain looked like noise on sweep)
Gain is 0.063V/V
While TL026 can be used as single ended output, to get best performance difference output should be used.
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