Features

Ultra-low noise performance; 10 kHz is 2.9 NV/ Hz at 10 kHz; 0.38 volt P-P, 0.1 Hz to 10 Hz; Performance; 12.5 volt/second conversion rate; 20 MG gain bandwidth products; THD 0.0002%@1 kinch; internal compensation income +5 (or -4) or greater excellent DC performance; maximum offset voltage 0.5 MV; The maximum input bias current of 250 paa; the minimum opening gain of 2000 V/MV; the EIA-481A standard.

Application

Sound; Optical diode and infrared detector amplifier; acceleration meter; low noise front placing large device; high -performance audio.

Product description

AD745 is an ultra -low noise, high -speed, FET input computing amplifier. It provides ultra -low -voltage noise and high -speed generally with bipolar input computing amplifiers and very low input current field effect tube input devices. The conversion rate of 20 MMB bandwidth and 12.5 volts/microseconds makes AD745 an ideal amplifier that requires low noise and high DC accuracy. In addition, AD745 does not show output phase reversal.

AD745 also has excellent DC performance. The maximum input bias current is 250 Pa, and the maximum bias voltage is 0.5 millivolo.

The internal compensation of AD745 is optimized for higher gain, providing higher bandwidth and faster conversion rate. This makes AD745 particularly useful as a front amplifier. Among them, the low level signal requires a amplifier that provides high -release large and wide bandwidth at the same time under these high gains.

AD745 has two performance levels. The rated temperature of AD745J and AD745K is within the commercial temperature range of 0 ° C to 70 ° C. It can be used in the 16 -lead SOIC packaging.

AD745 -Typical performance characteristics (@+25 c, vs 15 v, unless there are other instructions.)

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The performance amplifier performance JFET and bipolarity

AD745 provides industrial standards bipolar with low input voltage noise noise. The computing amplifier does not have its inherent input current error. As shown in Figure 3, it compares the input voltage noise and input source resistance of OP37 and AD745 OPAMPs. From this number, it can be clearly seen that under high source impedance, the low -current noise of AD745 also provides lower total noise. It is also important to note that using AD745, this noise reduction has been extended to low source impedance. AD745 lower DC current errorThe difference also reduces errors caused by offset and drift under high source impedance (Figure 4).

The internal compensation of AD745 is optimized for higher gain, providing higher bandwidth and faster conversion rate. This makes AD745 particularly useful as a front amplifier. Among them, the low level signal requires a amplifier that provides high -release large and wide bandwidth at the same time under these high gains.

Low noise circuit design

The input voltage noise performance of OPAMP is usually divided into two areas: broadband noise and low -frequency noise. AD745 provides excellent performance in both aspects. 2.9nv/hz@10kHz numbers are very good for JFET input amplifiers.

The noise from 0.1 Herz to 10 Hz is usually 0.38 micro-volt P-P. Users should pay attention to several design details to optimize low -frequency noise performance. Random airflow generates different thermocouple voltage, which looks like low frequency noise. Therefore, the sensitive circuit should be able to shield the airflow well. Keeping the absolute temperature of the chip is low and low -frequency noise can be reduced in two ways: first, the low frequency noise depends on the ambient temperature and increases to 25 ° C; second, due to the large gradient from IC to the environment, As mentioned earlier, noise generated by random airflow will be larger in terms of quantity. If possible, the chip temperature can be reduced by reducing the power supply voltage and using the appropriate card clip radiator.

Low -frequency current noise can be calculated through the size of the DC bias current:

and increased by 1/F power spectrum density to about 100Hz. For AD745, at 1kHz, the typical value of the current noise is 6.9FA/√. Use formula:

To calculate the resistance of Johnson noise (represented by current), you can see that the current noise of AD745 is equivalent to 3.45 current noise × 108 resistance.

Under high frequency, the current noise and frequency of the field effect tube increased proportional to the frequency. This noise is due to the real " part of the gate input impedance