Features

Low -dimensional voltage: maximum 60 μV

Extremely low offset voltage drift: maximum 0.7 μV/° C

Low input bias current: maximum 2 NA

Low noise: Typical 8 nv/√Hz

The smallest CMRR, PSRR, AVO GT; 120 db

Low power current: each amplifier 400 μA

Dual power operation: ± 2.5 V to ± 15 v

The unit gain stable

No phase reversal

Internal protection input beyond power supply voltage

Application

The control circuit of the wireless base station

Optical network control circuit

Instrument instrument

Sensor and control device

Thermocouple thermometer [123 ]

Resistance thermal probe (RTD)

Resistance bridge

Dialing current measurement

Precision filter

General description

[

123] The OPX177 series includes very high -precision, single, double, and four -way amplifier, with extremely low offset voltage and drift, low input bias current, low noise and low power consumption. The output is stable, the capacitor load is more than 1000 PF, and there is no external compensation. At 30V, the power current of each amplifier is less than 500 μA. The internal 500Ω series resistance is protected input, and the input signal level is allowed to exceed any power supply without phase reversal.

Unlike the high -voltage amplifier with extremely low bias voltage before,

OP1177 (single) and OP2177 (dual) amplifier uses micro 8 -lead surface stickers MSOP and MSOP and 8 Diversion narrow SOIC packaging. OP4177 (QUAD) provides TSSOP and 14 -drawing narrow SOIC packaging. In addition, the prescribed performance in MSOP and Tssop and the performance in SOIC packaging. MSOP and TSSOP only provide tapes and rolls.

The OPX177 series provides the widest temperature range specified in any high -precision amplifier in the surface packaging packaging. All versions are fully stipulated in the temperature range of 40 ° C to+125 ° C, and it is suitable for the most demanding operating environment.

The applications of these amplifiers include accurate diode power measurement, voltage and current level settings, as well as level detection in light and wireless transmission systems. Other applications include line power supply and portable row and control thermocouple, resistance temperature detector, strain bridge and other sensor signal regulation and precision filters.

pin configuration

Typical performance features

function description

OPX177 series is the fourth -generation simulation equipment company, industrial standard OP07 amplifier series. OPX177 is a high -precision, low noise computing amplifier, with extremely low disorder voltage and extremely low input bias current. Unlike the JFET amplifier, low bias and bias currents are relatively sensitive to the ambient temperature, even as high as 125 ° C.

The professional and linear design professional technology proprietary technology and linear design professional technology of analog device company produces a high-pressure amplifier that is better than OP07, OP77 and OP177 in a miniature MSOP 8-lead. Despite its small volume, OPX177 provides many improvements, including low broadband noise, very wide input and output voltage range, lower input bias currents, and no phase reversal at all.

The specified working temperature range of OPX177 is as wide as any similar device in the plastic surface installation package. This is becoming more and more important, because the size of the printing circuit board and the entire system is constantly narrowing, resulting in the increase in the temperature of the internal system. Compared with OP177, the power consumption is reduced by four times, and the bandwidth and conversion rate are doubled. Low power consumption and very stable performance also play a role in reducing the preheating drift error.

Under heavy negative load, the lineivity of the opening gain is better than the competitive parts, such as OPA277, which improves the DC accuracy and reduces the distortion in the high -closed loop gain circuit. Enter internal protection and is not affected by overvoltage conditions of any power supply track.

Like any high -performance amplifier, the maximum performance is achieved by following the appropriate circuit and PCB guide. The following sections provide practical suggestions to make full use of OPX177 under various application conditions.

Total noise-Including source resistance

OPX177's low input current noise and input bias current make it suitable for the circuit with a large amount of input source resistance. Each of the input bias voltage is increased by a maximum of 1 μV for each 500Ω source resistance.

The total noise density of OPX177 is:

:

EN is the input voltage noise density.

in is the input current noise density.

RS is the source resistance of the non -deduction end.

K is Bolitzman's constant (1.38 × 10 23 j/k).

T is an ambient temperature, and the unit is Kelvin (T 273+temperature unit is degrees Celsius).

When RS LT; 3.9kΩ, EN is subject to

When 3.9kΩ lt; RS LT; The heat noise of current noise and source resistance is a contribution of total noise.

When RS GT; 412 kΩ, current noise dominates, and

The total equal equal equalization of specific bandwidth is expressed as: [[[[[[[[[[ 123]

Among them, BW is a bandwidth of Hertz.

The above analysis is valid for the frequency greater than 50 Hz. When considering a lower frequency, flash noise (also known as 1/f noise) must be considered.

For reference for noise calculation, see the part of the KRC or Sallen key filter part.

gain lineivity

The gain lineivity reduces the error in the closed -loop configuration. The more straight the gain curve, the smaller the maximum error in the input signal range. This is especially true for circuits with high -closed loop gain.

OP1177 has a good gain linear even in the case of heavy load, as shown in Figure 51. Compare its performance with OPA277, as shown in FIG. 52. The two devices are measured under the same conditions, RL 2kΩ. OP2177 (double) has almost no distortion at a lower voltage. Compared with OPA277, the performance of OP1177 in different power supply voltage and different loads far exceeds OPA277.

Input overvoltage protection

When the input voltage exceeds the positive or negative power supply voltage, most amplifiers need to need External resistors to protect them from being damaged.

OPX177 has an internal protection circuit, which can apply a voltage of up to 2.5 V at a power supply at the input terminal of any terminal without any harmful effects.

If the voltage exceeds 2.5 V, a additional resistor that is connected to the input is used. The value of the resistor can be determined according to the formula:

In the case of OPX177 low input bias current less than 1 mAh, a 5,000 -Euro resistor and two inputs are Candidate can increase the input bias voltage of less than 5 volts, and the impact on the overall noise performance of the circuit can be ignored.

5 kΩ protection input voltage exceeds any power 27 V. For more information about noise and source resistance, see the THD+noise part.

The output phase reversal

The phase reversal is defined as the change of polarity in the amplifier transmission function. When the voltage of the input end is greater thanWhen the maximum co -mode voltage, many operational amplifiers will have phase reversal. In some cases, this may cause permanent damage to the amplifier. In the feedback loop, it may cause system lock or device damage. Even when the input voltage exceeds the power supply, OPX177 is not affected by the problem of phase reversal.

Settlement time

Stable time refers to the time required for the amplifier output to reach and maintain the percentage of its final value after the application input pulse. It is particularly important in the measurement and control circuit of the amplifier buffer ADC input or DAC output.

In order to minimize the stable time of the amplifier circuit, use appropriate power bypass and appropriate circuit element selection. The resistor should be metal film type, because their strange capacitors and inductances are smaller than the same type. The capacitor should be a polystyrene or polycarbonate type to minimize the medium absorption.

The power cord should be as short as possible to reduce the capacitor and inductance. The stability time of OPX177 is about 45 μs to 0.01%(1 MV).

overload recovery time

overload recovery refers to the time required for the output voltage of the amplifier from saturated to a linear response area. A common example is that the output voltage required by the circuit transmission function exceeds the maximum output voltage capacity of the amplifier. The 10 V input applied to the amplifier of the closed loop gain is the output voltage of 20 V. This exceeded the output voltage range of OPX177 at ± 15 V power supply, and forced the output saturation.

The recovery time is important in many applications, especially when the computing amplifier must delay the size signal under the large transient voltage.

FIG. 18 shows the positive overload recovery time of OP1177. After the driver is more than 100%, the output is restored within less than 4 μs.

The negative load recovery of OP1177 is 1.4 μs, as shown in Figure 19.

THD+noise

OPX177's total harmonic distortion is very low. This shows that the excellent gain linearity makes OPX177 the best choice for the high -closed cycle gain accuracy circuit.

FIG. 55 shows that OPX177 has about 0.00025%of the distortion of the unit gain, which is the worst configuration of distortion.

Capacity load driver

OPX177 is essentially stable under all gains, and can drive large capacitors load without oscillation. Without external compensation, OPX177 can safely drive up to 1000 PF capacitor loads under any configuration. Like almost any amplifier, in orderDrives a larger capacitance load under bit gain requires additional circuits to ensure stability.

In this case, the buffer network is used to prevent oscillation and reduce over -adjusting. One of the significant advantages of this method is that it has not reduced the output width because the resistance RS is not in the feedback loop.

FIG. 56 is a range snapshot of the OPX177 output response of 400 mm volt pulse. The load capacitor is 2NF. The circuit configuration is a positive unit gain, which is the worst situation of stability.

As shown in Figure 58, the R-C network is connected in parallel with the load capacitance (CL), which can drive the amplifier to drive a higher CL value without oscillation or overwhelming.

There is no bell, and the use of the buffer network will reduce the over -adjustment from 27%to 5%.

Table 5 lists the best values u200bu200bof RS and CS of several capacitance loads (maximum 200 NF). The values u200bu200bof other capacitance loads can be determined through experiments.

Note: Cushion technology cannot restore bandwidth loss caused by large capacitors.

Miscellaneous input capacitance compensation The effective input capacitor in the operation amplifier circuit (CT) consists of three components. These are internal differential capacitors between the input terminals, each input of the internal co -module capacitance of the ground, and an external capacitor including parasitic capacitors. In the circuit in FIG. 59, the closed -loop gain increases with the increase of the signal frequency.

The transmission function of the circuit is:

indicates zero

According to the values u200bu200bof R1 and R2 The cut -off frequency of closed -loop gain can be much lower than the cross frequency. In this case, phase margin (φm) will be severely degraded, causing excessive bell or even oscillation.

A simple way to overcome this problem is to insert a capacitor in the feedback path, as shown in Figure 60.

The poles obtained can be positioned to adjust the phase of the maneuver.

Set CF (R1/R2) CT to achieve a phase margin of 90 °.

Reduce electromagnetic interference

Many methods can be used to reduce the impact of electromagnetic interference on the amplifier circuit.

In one method, the strange signal on any input end is coupled to the opposite input end of the amplifier. The result is based on the co -mode inhibitory signal of the amplifier.

This is usually achieved by inserting a capacitor between the input end of the amplifier, as shown in Figure 61. However, this method may also lead to instability, depending on the capacitor value.

in a capacitorA resistor (see Figure 62) on the upper series can increase the gain of the DC circuit and reduce the output error. Place the breakpoint (introduced by R-C) under the secondary pole of the operation amplifier, which can improve the phase margin, thereby improving the stability.

According to the formula, R can be independent of C to select a specific phase of the badge

where:

A is the opening gain of the amplifier Essence

F2 is the frequency of A φm 180 ° phase.

Appropriate circuit board layout

OPX177 is a high -precision device. In order to ensure the best performance of the PCB level, it is necessary to be careful when designing the circuit board layout.

To avoid leakage, the surface of the circuit board should be kept clean and no water. The surface of the coating creates a moisture -proof layer and helps reduce parasitic resistance boards.

Keep the power trajectory short and bypass the power supply, which can minimize the power interference caused by changes in the output current, for example, when the exchange signal is driven to heavy load. The barrier capacitors should be as close as possible to the equipment power. Swiling capacitors are a problem with the output and input end of the amplifier. The recommended signal trace line is at least 5 mm to minimize the coupling of the power cord.

The temperature changes on the PCB can cause the Seebeck voltage of the solder joints and other different metal contacts to cause the thermal voltage error. In order to minimize the impact of the thermocouple, adjust the direction of the resistor and even heat the heat source evenly. The input signal path should contain the matching component number and type, and match the number and type of the thermocouple connector as much as possible. For example, virtual elements such as zero -value resistance can be used to match the actual resistance in the opposite input path. The matching parts should be located nearby and should be directed in the same way. Make sure the length of the lead is equal to the balanced state. Make the heat source on the PCB away from the amplifier input circuit as much as possible.

It is strongly recommended to use ground plane. The floor reduces the EMI noise, and it also helps maintain the constant temperature of the entire circuit board.

Differential amplifier

Differential amplifier is used in high -precision circuits to improve co -mode suppression ratio (CMRR).

In a single -meter amplifier (see Figure 63),

ratio R2/R1 and R4/R3 The non -matching between the co -mode suppression ratio is reduced.

In order to better understand this impact, we can consider definition,

Among them, ADM is a differential gain, and ACM is a co -model gain.

In orderIt must be proportional to the differential input signal.

From Figure 63,

arranged and combined with the previous equations:

The sensitivity of CMRR to R1 is obtained by the number of guidance of the CMRR in the equation 1.

Assume R (1+Δ)

CMRR errors in the worst case appear:

R1 R4 R (1+Δ) and R2 R3 R (1 Δ; Δ )

You can get these values u200bu200bon the replacement of these values:

where Δ is the tolerance of the resistor.

The lower tolerant value resistance leads to higher co -mode suppression (the co -mode suppression ratio of the high -end operational amplifier).

With a 5%tolerance resistance, the maximum co -mode suppression ratio can be guaranteed to be 20 decibels. Alternatively, using a 0.1%tolerant resistance can produce a co -mode suppression ratio of at least 54DB (assuming the operational amplifier CMRR × 54DB).

When the co -mode suppression ratio of OPX177 is the minimum of 120 decibels, the resistance matching is the restricted factors of most circuits. Fine -adjustable resistance can be used to further improve the resistance matching and co -mode suppression ratio of the differential amplification circuit.

High -precision thermocouple amplifier

The thermocouple is composed of two different metal wires in contact with. Different metals generate voltage

In the formula:

TJ is the temperature during the measuring point measurement.

TR is a cold temperature.

α is a unique to the Seabak coefficient unique to different metals used in thermocouple.

VTC is the voltage of the thermal power, which becomes larger as the temperature rises.

The maximum measurement accuracy requires the cold end compensation of the thermocouple. In order to perform cold -end compensation, a copper wire short circuit was applied at the terminal connection (inside the temperature block) to simulate 0 ° C. Use R5 to fine -tune the resistor to zero the output voltage, and then remove the copper wire.

OPX177 is an ideal amplifier of the thermocouple circuit because it has very low disorders, excellent PSRR and CMRR, and low -frequency and low noise.

It can be used to create a well -linearized armocouple circuit. The resistor R1, resistor R2, and diode D1, as shown in Figure 64, installed in the equivalent block.

Low -power linear RTD

The common application of a single component change bridge is the RTD thermometer large, as shown in Figure 65. The excitation is transmitted to the bridge by the 2.5 V reference voltage applied to the top of the bridge.

The thermal resistance of RTD can be as high as 0.5 ° C to 0.8 ° C/mW. In order to minimize the error caused by the drift of the resistor, the current of each branch of the bridge must be kept at a lower level. In this circuit, the amplifier supply current flows across the bridge. However, when the maximum power supply current of OPX177 is 600 μA, even at the highest resistance, the RTD consumption power is less than 0.1 mW. The error caused by power loss in the bridge is kept below 0.1 ° C.

By adjusting the RP, the bridge is calibrated at the minimum value of the temperature to be measured until the output is zero.

To calibrate the output range, set the standard and linear potential meter to the middle point, and apply a temperature of 500 ° C to the sensor, or replace the equivalent 500 ° C RTD resistor.

The full marking potential meter was adjusted to 5 V output. Finally, the resistance of a 250 ° C or an equivalent resistor is applied, and the linear potential meter is adjusted to 2.5 V output. The adjustment of the adjusted circuit is better than ± 0.5 ° C.

Single -transportation bridge

The low input offset voltage drift of OP1177 makes it very effective for the bridge amplifier circuit for RTD signal conditioning. Compared with the instrument amplifier, using a single bridge operational amplifier is usually more economical.

In the circuit shown in FIG. 66, the output voltage of the operation amplifier is:

In the formula, Δ ΔR/R is due to the resistance temperature The temperature changes of the detector, the resistance of the resistor's resistance to the resistance of the bridge.

For Δ lt; lt; 1, the previous expression became

In VREF constant, the output voltage and gain factor Δ linear relationship [123 123 [123 ]

The implementation of the active filter

The low offset voltage and high -co -model suppression ratio make it the best choice for precision filter, as shown in FIG. 67. This filter can independently adjust the gain and cut -off frequency.

Because the co -mode voltage entering the amplifier changes with the input signal in the KRC filter circuit, the high -co -model suppression ratio is needed to reduce distortion. In addition, when the circuit gain selection is high, the low offset voltage of OPX177 allows a wider dynamic range.

The circuit of FIG. 67 includes two stages. The first level is a simpleThe high -pass filter, where the corner frequency (FC) is:

and

Among them, K is DC [123 ]

Choosing an equal capacitance value to minimize sensitivity, and simplify the equivalent 2 to:

The Q value determines the peak of gain and frequency (transient response (transient response Ring in the middle). The Q value that is usually selected is usually close to unification.

Set

to generate minimum gain peak and minimum bell. Use Formula 3 to determine the values u200bu200bof R1 and R2.

For

, R1/R2 2 in the circuit example. For simplicity, select R1 5 kΩ and R2 10 kΩ.

The second level is a low -pass filter, where the corner frequency can be determined in a similar way. For R3 R4 R.

and

Channel separation

usually needs to use multiple amplifiers on a single chip to refuse any signal input or output from adjacent channels Essence OP2177 input and bias circuit design is used to prevent the signal from from one amplifier channel to another channel. Therefore, OP2177 has an impressive channel interval with a frequency of 100kHz greater than 120db, and the signal is greater than 115dB when the signal is as high as 1MHz.

Character size