Features

Very low noise, 5 nv/hz@1 kHz

Good input Body bias voltage, maximum 0.4mv

Low offset voltage drift, maximum 2 μ v/℃

[123 ] Very high gain, minimum 1000 V/MV

Over 110 decibel

Conversion rate, 2V/μs typical value

gain bandwidth multiplication, 6 mHz typical value

Industrial standards Four Yin feet

Provide it in the form of mold generally explained

OP470 is a high -performance single -chip four -way computing amplifier, It has extremely low voltage noise, 5NV/Hz, maximum 1kHz, and the performance is equivalent to the ADI industry standard OP27.

OP470 is characterized by the input offset voltage of less than 0.4 millivolo, which is very suitable for the four -way computing amplifier, and the offset drift is lower than 2 millivolttime/∞C to ensure that the entire military temperature range. OP470's opening gain exceeds 10,000,000 under 10 KW loads, even in high -gain applications, it also ensures excellent gain accuracy and linearity. The input bias current is less than 25NA, reducing errors caused by signal source resistance. OP470's CMR is more than 110dB, and PSRR is less than 1.8mv/V, which significantly reduces errors caused by ground noise and power fluctuations. The power consumption of the four -way OP470 is half of the four OP27, which is a significant advantage for the application of power consumption. OP470 is a stable unit gain, the width of the gain band is 6MHz, and the conversion rate is 2V/ms.

OP470 provides excellent amplifier matching, which is very important for applications such as multi -profit blocks, low noise meter amplifiers, four buffers, and low noise active filters.

OP470 meets industry standards 14 lead immersion. It is compatible with LM148/149, HA4741, HA5104, and RM4156 four -way computing amplifier pins, which can be used to upgrade systems that use these devices.

For higher speed applications, it is recommended to use OP471 with a conversion rate of 8V/MS.

pin connection

Simplify the schematic diagram

Dice features

OP470 -typical performance features

]

Application information

Voltage and current noise

OP470 is one The four -way operation amplifier with a very low noise. At 1 kHz, the typical voltage noise is only 3.2 NV ÷ Hz. Because the voltage noise is inversely proportional to the square root of the collector current, the extremely low noise characteristic part of the OP470 is achieved by operating input transistors by operating in the high set electrode current. However, the current noise is proportional to the square root of the collector current. Therefore, the excellent voltage noise performance of OP470 is at the expense of current noise performance, which is a typical characteristic of a low noise amplifier.

In order to obtain the best noise performance in the circuit, the relationship between voltage noise (EN), current noise (in) and resistance noise (ET) must be understood.

Total noise and source resistance

The total noise of the operation amplifier can be calculated through the following formulas:

In the formula:

[

123] EN u003d Total input Reference noise

EN u003d Shanganpei voltage noise

in u003d operation amplifier current noise

ET u003d source resistance heat noise

RS u003d source resistance

The total noise refers to the input terminal, and the noise at the output end will amplify the circuit gain. Figure 4 shows the relationship between the total noise and source resistance when 1kHz. For RS LT; 1 KW, the total noise is controlled by the voltage noise of OP470. When RS rises to more than 1kW, the total noise increases, mainly controlled by resistance noise, not the voltage or current noise control of the OP470. When RS exceeds 20kW, the current noise of OP470 becomes the main contributor of total noise.

FIG. 5 also shows the relationship between total noise and source resistance, but at 10 Hz. Due to the inverse ratio of current noise and frequency, the total noise is faster than in Figure 4. In Figure 5, when RS GT; 5KW, the current noise of OP470 accounted for the leading position of total noise.

From Figure 4 and Figure 5, it can be seen that in order to reduce the total noise, the source resistance must be kept at the minimum. In applications with high source resistance, OP400, which has lower current noise compared to OP470, will provide lower total noise.

FIGThe relationship between peak noise and source resistance within the range of Hz to 10Hz. Similarly, when the RS value is low, the voltage noise of the OP470 is the main contributor of the noise in the peak, and the current noise is the main contributor when the RS increases. The intersection of the noise between the peak between OP470 and OP400 is RS u003d 17 kW.

OP471 is a higher -speed version of OP470, with a conversion rate of 8V/MS. OP471's noise is slightly higher than OP470. Like OP470, OP471 is stable in unit gain.

Table one lists a typical source resistance of some signal sources for reference.

Noise measurement. The circuit in FIG. 7 in FIG. 7 is a test device that measures the peak voltage noise. To measure the 200 NV peak noise specifications of OP470 within the range of 0.1 Hz to 10 Hz, the following preventive measures must be complied with:

1. The device must be warm up at least five minutes. As shown in the preheating drifting curve, due to the increase in the temperature of the chip after power, the offset voltage usually changes 5 mv. Within 10 seconds of measurement intervals, the effects caused by these temperatures can exceed dozens of millivolves.

2. For similar reasons, the equipment must be shielded well. The shielding can also minimize the impact of the thermocouple.

3. Sudden exercise near the device can also ""feed"" to increase the observed noise.

4. The test time of measurement of 0.1 Hz to 10 Hz noise should not exceed 10 seconds. As shown in the response curve of the noise test instrument, the 0.1 Hz corner is only defined by one pole. The 10 -second test time is used as an extra pole to eliminate the noise contribution of the frequency band below 0.1.

5. When measuring the noise on a large amount of device, it is recommended to perform the noise voltage density test. 10 Hertz noise voltage density measurement value is very correlated with the noise reading between 0.1 Herz to 10 Hzhn peaks, because these two results are determined by the position of white noise and 1/f angle frequency.

6. Power on the test circuit through a good bypass low -noise power supply (such as battery). This will minimize the output noise introduced by the amplifier power pins.

Noise measurement-noise voltage density

The circuit in FIG. 9 shows a method of rapid and reliable measurement of the noise voltage density of the four-way computing amplifier. Each separate amplifier is connected in series and gains in the unit. The last amplifier is preserved at non -mutual gain 101. Because the AC noise voltage of each amplifier is irrelevant, they increase in the form of a common root root, which generates:

OP470 is a single -chip device with four same amplifiers.

The noise voltage density of each separate amplifier will be matched to give:

noise measurement-current noise density

Figure 10 in FIG. 10 The testing circuit shown can be used to measure the current noise density. The relationship between the voltage output and the current noise density is:

in the formula:

G u003d get 10000

RS u003d 100 kW source Resistance

Consideration of capacity load driving and power supply

OP470 is a unit gain stable, which can drive large capacitors load without oscillation. Nevertheless, it is strongly recommended to bypass good supply. Proper power bypass can reduce problems caused by the noise of the power cord and improve the capacitor load driving capacity of OP470.

In the standard feedback amplifier, the output resistance of the computing amplifier is combined with the load capacitance to form a low -pass filter, which adds phase shift and reduce stability in the feedback network. Figure 11 shows a simple circuit to eliminate this impact. The increased component C1 and R3 make the amplifier and the load capacitance decoupled, and provide additional stability. The C1 and R3 values u200bu200bshown in Figure 11 are suitable for load capacitors up to 1000pf when used with OP470.

In the application of the inverter or non-inverse input of OP470, in applications driven or grounded by low power impedance (below 100 W), if V+is applied before V-, Or when V is disconnected, excessive parasitic current produces. Most applications use dual -tracking power supply, and the equipment power pins are bypass appropriately, and there will be no problems with power. If the V-is disconnected and the source resistance connected in series is at least 100 W (Figure 11), the parasitic current will be limited to the level of safety. It should be noted that any source resistance, even if it is 100 watts, will add noise to the circuit. Where the noise requirements are kept at a minimum, the 锗 or Schottky diode can be used to restrain the V -type tube foot and eliminate the parasitic current instead of using series restrictions. For most applications, each board or system only needs to clamp one diode.

Unit's gain buffer application

When the RF is 100 W, the input is driven by fast, large signal pulse ( gt; 1 v), the output waveform is shown in Figure 12.

In the similar fast -feding part of the output, the input protection diode effectively receives the output to the input terminal, and the signal generator will generate only short -circuit protection restrictions. Current. RF is 500 watt -hour, the output can process the current requirements (at 10 volts IL LT; 20 mAh); the amplifier will remain in its activation mode and will transition smoothly.

When RF GT; 3KW, an extra phase shift and reduced phase margin formed by the input capacitor (2PF) of the RF and the amplifier. Small capacitors (20 PF to 50 PF) with RF help to eliminate this problem.

Application

Low noise amplifier

FIG. 13 shows a simple way to reduce the noise of the amplifier through parallel amplifier. The noise of the amplifier, as shown in Figure 14, is about 2 nv/hz@1 kHz (R.T.I.). The gains of each parallel blee and the entire circuit are 1,000. 200 watt resistance restricted circular current, and provided 50 watts of effective output resistance. The amplifier is stable under the capacitance load of 10 mA, and it can provide an output driver up to 30 mAh.

Digital shaking control

Figure 15 Use a DAC-8408 four-bit 8-bit DAC in two channels Signals between them. Two of the four DACs of the complementary DAC current output DAC-8408, the driver is driven by a single four OP470 current voltage converter. The amplifier has complementary output, and its amplitude depends on the digital code applied to DAC. FIG. 16 shows the 1KHz input signal and the complementary output of the digital slope applied to the DAC data input. The distortion of digital shaking control is less than 0.01%.

By using the feedback resistor inside the DAC, it eliminates the internal DAC trapezoidal resistor and the current voltage feedback resistor. The gain error caused by matching. Among the four DACs available in DAC-8408, only two DAC (A and C) actual transmission signals can be used. DAC B and D are used to provide additional feedback resistors required in the circuit. If VREFB and VREFD input remain unconnected, the current voltage converter using RFBB and RFBD is not affected by digital data of DAC B and D.

The noise amplifier

The circuit in FIG. 17 is a simple noise amplifier. When the input signal is lower than the default limit, the FET switch is cut off the output.

The input signal is sampled by a peak detector, and the time constant is set by C1 and R6. When the output of the peak detector (VP) is lower than the threshold voltage (VTH) set by R8, the comparator composed of computing amplifier C switches from V-to V+. This will drive the grid of the Credit Tube of the Nutra field effect, open it, and reduce the gain of the inverter amplifier formed by the operation amplifier A to zero.

Five -band low -noise stereo -graphic balancer

The graphics balancer circuit shown in FIG.For 3V RMS input, the signal -to -noise ratio on the 20KHz bandwidth is better than 100dB.The larger inductors can be replaced by the active electrical sensor, but this will reduce the signal -to -noise ratio.

The size of the shape