Features

● Large signal bandwidth: 150MHz (AP), 200MHz (AU) (voltage feedback)

● High output current: ± 70ma

● conversion rate : 1500V/μs (AP), 1700V/μs (AU)

● Differential gain: 0.15%

● Differential phase: 0.08 °

● Excellent bandwidth/power supply Current ratio: 200MHz/5mA

● Low input bias current: --1.2μA

Application

● Broadcast/HD TV equipment

● Communication [ 123]

● Pulse/RF amplifier

● Active filter

● High -speed analog signal processing

Digital video signal

Instructions

OPA622 is a single -chip amplifier component, which is designed for precision broadband systems, including high -resolution video, radio frequency and intermediate frequency circuits and communication devices. It includes a single -chip integrated current feedback computing amplifier block and voltage buffer block. After the combination of the two, the voltage feedback computing amplifier is formed.

When a current feedback amplifier combination, it provides a large signal bandwidth of 280MHz and a conversion rate of 280MHz at the ± 2.5V output level. Output buffer grade outputable output current. The high output current capacity allows OPA622 to drive two 50 or 75 to make it have the ideal choice of radio frequency, intermediate frequency and video applications.

The feedback buffer provides 700MHz bandwidth, extremely high conversion rate and very short signal delay time. It is mainly used for inter -baptism, not driving long cables. When combined with the current feedback amplifier, OPA622 can be used as a voltage feedback amplifier input with two same high impedance. The input configuration has a low -joint gain, low input offset, and due to the delay time of the additional feedback buffer, the bandwidth is reduced compared with the current feedback configuration. Unlike the ""classic"" computing amplifier, OPA622 achieves almost constant bandwidth within a wider gain and output voltage range. ROG's open -loop gain external settings avoid a large compensation capacitor, increase the conversion rate, and allow frequency to respond to various gains and load conditions.

Dice information

Typical performance curve

Voltage feedback amplifier (Figure 5) [123 123 ] VCC u003d ± 5V, IQ u003d ± 5mA, GCL u003d+2V/V, RLOAD u003d 100 , RSOURCE u003d 50 , RQ u003d 430 , ROG u003d 150 25 ° C, unless there are other regulations.

Input protection For MOSFET devices, the necessity of preventing static damage has long been recognized, but all semiconductor devices should be protected by this potential destructive source. OPA622 integrates the ESD protection diode in the film, as shown in Figure 1. These diodes do not require external protection diode, which will increase capacitors and reduce communication performance. As shown in the figure, all input tube feet of OPA622 are protected by any power supply through a pair of back -to -back diode. When the input voltage exceeds any power of about 0.7V, these diode starts to turn on. This happens when the signal source still exists and the amplifier loses the power. The diode can usually bear the continuous current of 30mA without damage. However, in order to ensure long -term reliability, the diode current should be limited to about 10mA as much as possible from the outside.

The design of the internal protection diode can withstand 2.5kV (using human models) and will provide sufficient ESD protection for most normal operation processes. However, static damage may cause subtle changes in the input characteristics of the amplifier, not necessarily damaged the device. In the precision amplifier, this change will significantly reduce the offset and drift. Therefore, when dealing with OPA622, it is strongly recommended to take anti -static measures.

Performance Discussion

OPA622 provides a full -power bandwidth that was not available in single -chip device before. In addition, the work of the amplifier decreases static. The flexibility of OPA622 design provides the speed advantage of the current feedback amplifier or the accuracy advantage of voltage feedback amplifier. Programmable static current characteristics also help to make the amplifier meet specific design requirements.

FIG. 2 shows the simplified circuit diagram of OPA622. It contains four main parts: bias circuit, OTA, output buffer and feedback buffer.

Partial pressure circuit

The static current of the partial control signal processing level of the partial circuit is allowed to be used to connect from the pink 2 to -vcc resistor RQ to set the external static current and set the cross -guided by the amplifier. And use its temperature characteristics to maintain constant cross -guidance within the temperature range. Static current control small signal bandwidth and communication behavior. The static current specified in OPA622 is ± 5mA, RQ u003d 430 . The scope of recommended is ±3 mAh to ± 8 mAh.

Application circuit usually does not show resistance RQ, but it is necessary for normal work.

Under the fixed RQ, the static current increases with the temperature (see the typical performance curve). Static currents are relatively constant with temperature changes with temperature changes. You can also change the static current through external control signals or circuits. Figure 3 shows the use of TTL compatible logic electric flats to disable OPA622. 0V/5V logic levels are converted to 1MA/0MA current to connect to pinnacle 2. The current flowing into the RQ increases the voltage of the pins 2 to the -VCC rail about 1V, thereby reducing the IQ to close to zero, and disable OPA622.

OTA and output buffer parts

The computing cross -guide amplifier (OTA) and output buffer are the basic components of the current feedback amplifier. The current feedback configuration of OPA622 is shown in Figure 4. OTA is composed of complementary launch pole followers and subsequent complementary current mirrors. The voltage at the high impedance+IN terminal is transmitted to the BUF+input/output terminal at low impedance. If the current flows into or out of the BUF+terminal, the complementary mirror reflects the current to the OTA terminal. The current of the high impedance OTA terminal is determined by the voltage between the+in and the BUF+terminals and the cross -guided product. The output buffer part is an open ring buffer composed of a complementary emitter. It is designed to drive cables or low impedance loads. The output of the buffer is not limited or protected by current. As shown in Figure 4, the feedback network of current feedback amplifier is used between VOUT and BUF+terminals. Figure 8 illustrates the bandwidth of various output voltage configuration of the current feedback.

Feedback buffer

OPA622 This part is the same complementary emission pole as the input buffer in the OTA part. It is designed for a baying buffer instead of driving long cables or low impedance loads. When the feedback buffer is used as an independent device, it is recommended that the minimum load resistance is 500 Feedback buffer output is not limited or protected by current. The bandwidth of the feedback buffer is shown in Figure 7.

Configuration

Voltage feedback amplifier

OPA622's internal design is different from the ""classic"" computing amplifier structure, but it can still be used for all traditional operational amplifiers applications. Like the traditional operational amplifier, the feedback network controls the closed -loop gain (GCL) connected to the reverse input. However, in OPA622, the resistance ROG also adapts to closed -loop gain at the same time, optimizing the frequency response and stability.

The ""classic"" differential input level consists of two identical transistors and a transmitting polar degradation resistor, two current sources, and a active load diode. However, the classic configuration limits the current through the current of the gain crystal tube, and the current provided by the current sourceMake a prevailing.

In the new design, a complementary push -pull buffer (shooting pole follower) replaces the side of the differential level without the offset of 0.7V. The feedback buffer is the second complementary emission pole follower, and connects to the rot gain resistance ROG between the output end, and reproduces the disadvantage of the differential level. There is no shortage of classic design. The current of the charging of the parasitic capacitor at the bottom of the gain crystal is no longer limited to the fixed current of the current source, but is directly proportional to the input signal. The result of this improvement is about 10 times the better conversion rate.

The amplification current of the gain crystal tube of one buffer is an output current. OTA's high impedance output is now buffer by high current output level. This class is used to drive long cables or low impedance loads at full power.

The same input buffer reduces the input offset to usually less than ± 7 μV. The closed -loop output offset is usually caused by the NPN and PNP transistor in the OTA image and do not match the output bias current.

FIG. 5 illustrates the circuit structure of the voltage feedback amplifier in the complementary circuit design. The feedback buffer and OTA input buffer constitute a differential input. Insert feedback buffer converts the current feedback shown in Figure 4 to the voltage feedback shown in Figure 5.

The resistor ROG sets up the loop gain, and corresponds to the transmutation resistor in the classic differential class. Because the ROG resistance can change external changes, a flat frequency response can be achieved within a wide range of applications without using a capacitor to compensate the amplifier. Compared with the current feedback amplifier, the feedback resistance can be used to adjust the closed -loop gain, and ROG independently adjusts the opening of the ring to optimize the frequency response.

Unlike the ""classic"" computing amplifier structure, the structure of the OPA622 enables it to obtain almost constant bandwidth to achieve different closed -loop gains, as well as improved frequency response and large signal behavior. In addition, unlike the current feedback computing amplifier, it provides two the same high impedance input, lower input offset values, and improved coexistence suppression ratios.

current feedback amplifier

FIG. 4 shows the current feedback configuration. The BUF+terminal from the feedback loop from the output to the OTA segment is closed. The short feedback loop of the no -feedback buffer has a wider current feedback concept bandwidth. The difference between the AC performance between the voltage and the current feedback by the additional signal delay time of the feedback buffer is determined.

The specifications of offset voltage, coordinate measuring machine and stable time are more compromised.

The opening gain of the current feedback amplifier directly changes with the closed -loop gain, and can be adjusted by changing the size of the R2 | R1. For the gain of less than 10V/V, you can adjust the opening of the ring to obtain a bandwidth that has nothing to do with gain, but when the second -order effect starts to dominate, the effect of this adjustment will be limitedEssence

FIG. 6 gives an overview of OPA622 inverter and non -inverter ballast configuration, and shows the equations of a closed -loop gain.

The best frequency response adjustment is adjusted

Traditional voltage feedback computing amplifier uses a compensation capacitor to stabilize the unit gain operation. During the conversion process, the static current is charged and discharged to the capacitor. The two parameters determine the conversion rate according to the following conditions:

This method is not suitable for broadband computing amplifiers. Depending on the gain bandwidth, the conversion rate and large signal behavior are significantly reduced, and the bandwidth decreases with the increase of the closing loop gain.

The amplifier with external compensation capacitors allows the optimal frequency adjustment relative to a closed -loop gain, but it does not significantly improve the big signal behavior. The most effective solution is to make the open -loop gain (GOL) adjustable outside.

The widely used current feedback computing amplifier adopts a real -complementary circuit technology design, overcoming the internal compensation capacitance, and allowing the feedback network to set the opening gain. The ratio of the feedback resistance determines the low -frequency closed -loop gain, and the intermodal resistance determines the open loop gain of the amplifier stable work and the frequency response. A almost constant bandwidth can be achieved within a wide closed -loop gain range. However, there are problems such as inconsistent input, input offset, and co -mode suppression ratio of current feedback computing amplifiers. The complementary topology of the voltage feedback amplifier OPA622 has two identical high impedance input, lower input offset values u200bu200band improved CMRR. The ratio of the feedback resistance determines the low -frequency closed -loop gain, and the external resistance ROG sets the opening of the ring to achieve a flat frequency response at a wide closed -loop gain range. Because ROG can be selected, even if the load capacitance is larger, the optimized pulse response is possible. OPA622 combines the conversion rate enhancement function of the complementary amplifier design with the accuracy of the voltage feedback system.

The hybrid model shown in FIG. 9 describes the communication characteristics of non -compensation broadband differential operations amplifiers. The opening frequency response of the various ROG values u200bu200bshown in Figure 10 is determined by two time constants. The component R and COTA between the current source output and the output buffer form the first opening pole TC. The signal delay time simulated in the output buffer combines several small phase movement time constant and delay time. They are distributed in the entire amplifier and also exist in the feedback circuit. As shown in Figure 10, increasing ROG will lead to a decrease in the opening of the ring. The ratio of two time constant TC and TD of the two -time response of the opening frequency also determines the product of the optimal closed frequency response.

TC and TD are fixed by the designed amplifier. The purpose of ROG is to change GOL and GCL to maintain the product GOL u0026#8226; GCL constant, which is the best and gain and independent frequencyTheoretical conditions of rate response. Figure 11 summarizes some of the best plane closed -loop responses and points out the ROG value. It should be noted that the bandwidth is relatively constant, and the ROG has the highest value (low -opening gain) at a low -closed loop gain. With the increase of the opening gain, the harmonic distortion has also improved. Figure 12 shows the frequency response of OPA622 under GCL u003d+2V/V and variable ROG to prove its effect on the flat frequency response. ROG's tiny changes may require compensation load capacitors. It is possible to achieve the best pulse in the large range of load capacitors, and there will be no excessive ring and bell. For example, FIG. 13 shows the selection curve of the best ROG value and+2V/V gain (GCLO) down load capacitance.

Thermal factors

OPA622 does not need a radiator in most environments. However, the heat sink will reduce the internal heat, which makes it work cooler and reliable. Under extreme temperature and full -load conditions, the radiator is necessary. The internal power consumption is given by the formula PD u003d PDQ+PDL. Although PDQ is very low (VCC u003d ± 5V is 50MW), be careful when the signal is applied. For high -speed computing amplifiers, a more accurate method for determining power consumption is to measure the average static current under several typical load conditions. The power consumption of OPA622 is affected by the signal type and frequency, output voltage and load resistance, and the duplication rate of signal conversion. FIG. 14 shows the relationship between the total average power supply current and the sine wave frequency under different output voltage. Figure 15 shows the relationship between the total static current and the repetitive frequency of the application square wave signal.

Circuit layout

The physical layout of the printing circuit board will greatly affect OPA622's high -frequency performance. The following is an absolute suggestion. These are typical issues of high bandwidth, low bandwidth, low bandwidth.

u0026#8226; The power supply is very close to the device pin. Use a pyramid capacitor (about 2.2 μF) and parallel 470pf ceramic capacitor. It is recommended to use the surface paste because of their low inductance. u0026#8226; PC board marks of the power cord should be wider to reduce the pedal. u0026#8226; short, low -inductance trajectory. The entire physiological cycle should be as small as possible.

u0026#8226; use low impedance flooring on the part side to ensure that there are low impedance grounding in the entire layout.

u0026#8226; Put the ROG resistor as close to the packaging as much as possible, and use the short line length as possible.

u0026#8226; Do not extend the ground layer to high impedance nodes sensitive to strange capacitors, such as the input and ROG terminal of the amplifier.

u0026#8226; It is not recommended to use sockets because they increase significant inductance and parasitic capacitors. If you need a socket, use the zero section without welding socket.

u0026#8226; use low inductance and surface installation components to prevent communication performance.

u0026#8226; Strictly recommend the use of resistors (50 to 330 ) with high impedance input series to ensure stable operation.

u0026#8226; Insert prototype board and winding board will not work properly. A clean layout is essential to use radio frequency technology.

Recommended component value

Table 1 summarizes the recommended component value of the best flat frequency response. Use 100 load resistance and 2PF load capacitance to determine the recommended value. It may need to adjust the circuit value, especially when the load capacitance is high. According to the behavior shown in FIG. 12, when the ROG is reduced, the frequency response will peak. When the ROG increases, the frequency response will gradually decay. The COTA capacitor is responsible for the first opening of the ring, and requires a small external capacitor to obtain the gain of+1V/V and+2V/V to ensure stable operation. The packaging pin, the internal lead frame and the connection line constitute the resonant circuit. In the range of 150 to 390 the resistor within the range and all high impedance input series will be damped to the encapsulated resonant circuit. In addition, the feedback resistor R1 is connected with high impedance input. DIP packaging suggestion R1 ≥ 330 , SO packaging suggestion R1 ≥150 .