Features

Display delay: 1.9ns

Bandwidth:

- OTA: 710MHz

- Comparison device : 730MHz

Low input bias current: ± 1 μA

Sample and keep switching transients: ± 5mv

sampling sampling Keep feed inhibition: 100db

Charging injection: 40FC

Keep command delay time: 2.5ns

TTL/cmos Keep control

Application

Broadcast/HD TV equipment

Telecom equipment

high -speed data collection [ 123]

CAD monitor/CCD image processing

nano seconds vein volume device/peak detector

pulse coding modulator/ Smart

Complete the video DC level recovery

Sample to keep the amplifier

SHC615 upgrade

Explanation

OPA615 is a complete subsystem that is used for low -frequency buzzing sounds for very fast and accurate DC recovery, bias clamps and broadband amplifiers or buffers. Although it is designed to stabilize the performance of the video signal, it can also be used as a sampling to maintain the amplifier, a high -speed integralor, or the naming pulse peak detector. This device has a broadband computing cross -guidance amplifier (OTA), and has a high impedance co -source grid current output and a fast and accurate sampling comparator. Together, it has set new standards for high -speed applications. OTA and sampling comparators can be used as independent circuits, or they can be combined into more complex signal processing levels. The self -partial voltage bipolar OTA can be regarded as an ideal voltage control current source, and optimized the low input bias current. The sampling comparator has two identical high impedance input terminals and an current output end optimized for low output bias current and bias voltage; it can be controlled by TTL compatible with TTL compatible in several seconds. OTA and sampling comparators can be adjusted through external resistors, so as to optimize the balance of bandwidth, static current and gain.

OPA615 has SO-14 surface installation and MSOP-10 package.

block diagram

pin configuration

Typical features

TA u003d+25 ° C, IQ u003d 13ma, unless otherwise explained.

OTA

SOTA ]

Performance Discussion

OPA615 contains a broadband computing transgender amplifier (OTA) and a fast sampling comparator (SOTA) It represents a complete subsystem for very fast and accurate DC recovery, offset clamping, and correction of GND or adjustable reference voltage, as well as low -frequency buzzing sounds for broadband computing amplifiers or buffer amplifiers. Although the integrated circuit is designed to improve or stabilize the performance of broadband video signals, it can also be used as a sampling to maintain the amplifier, high -speed integralor, nanosecond pulse peak detector or related dual sampling system a part of. Broadband computing transgender amplifier (OTA) has high impedance co -grid current output and rapid and accurate sampling comparator, which provides new standards for high -speed sampling applications. OTA and sampling comparators can be used as independent circuits, or combined to create more complex signal processing levels, such as sampling and maintaining amplifiers. OPA615 simplifies the designs of clamps or DC recovery levels in the input amplifier, professional broadcasting equipment, high -resolution CAD monitors and information terminals in the information terminal, and signal processing levels of nanosecond pulse energy and peak. The device also simplifies the design of the high -speed data collection system behind the CCD sensor or the front number converter.

The external resistance RQ on the package of SO-14 allows users to set static current. RQ is connected from pins 1 (IQ adjustment) to -vcc. It determines the working current of the OTA part to control OTA's bandwidth and communication behavior and cross -guidance.

In addition to the static current setting function, the power current control of the absolute temperature (PTAT) of the absolute temperature will increase the relationship between static current and temperature. This change keeps relatively constant temperatures from the transgender (GM) of OTA and comparators. The circuit parameters listed in the specification table are measured in the case of RQ set to 300 and provide nominal static currents under 13mA. There is no need to use the current of R300Ω in the static circuit, and in this case, there is no need to always use the current R300.

Operation cross -guidance

The amplifier (OTA) section and overview

chapters and overview

The symbols of the part of the OTA are similar to the symbols of the bipolar transistorsAnd self -partial pressure OTA can be regarded as a quasi -ideal transistor or pressure control current source. The appearance and operation of the application circuit used for OTA is very similar to that of the transistor circuit bipolar crystal is also a voltage control current source. Like the crystal tube, it has three terminals: a high impedance input (base pole), and a low input bias current of 0.3μA optimized input/output (transmitting pole) and high impedance current output (set electrode).

OTA consists of a complex buffer and a subsequent complementary current mirror. The buffer ballast uses the Dallington output stage, and the current mirror has a class linked output. The addition of this co -source grid circuit increases the current output resistance to 1.2m This function improves OTA linearity and driving capabilities. Any bipolar input voltage has the same polarity and signal level at a low impedance buffer or transmitting polar output at a high impedance base. For the opening diagram, the emission pole is connected to the GND; the voltage between the setting electrode current is determined by the voltage between the basis and the emission pole. In the application circuit (Figure 36B), the resistance RE between the transmitter and GND is used to set the OTA transmission characteristics.

The following formula describes the most important relationship. RE is the output impedance of the buffer (transmitter) or the countdown of OTA transdifinder. More than ± 5mA or more, the collector current IC will be slightly less than the value shown in the formula.

The RE resistor can bypass the relatively large capacitors to maintain a higher AC gain. The parallel combination of RE and this large capacitor forms a high -pass filter, which increases high -frequency gain. In some cases, the RC compensation network may be required to work in parallel to optimize high -frequency response. The large signal bandwidth (VO u003d 1.4VPP) measured on the transmitted end reaches 770MHz. The frequency response of the collector is directly related to the resistance value between the set and ground; it decreases as the resistance value increases, which is due to the low -pass filter formed by OTA C output capacitors.

FIG. 35 shows the simplified box diagram of OPA615 OTA. Both the transmission pole and the setting electrode output provide ± 20mA driving capacity for driving low impedance loads. The emission pole output is not limited or protected by current. Avoid short circuits on the ground, but it is unlikely to cause permanent damage.

Although the OTA function and the mark look similar to the crystal tube, it provides essential differences and improvements: 1) For the positive B-To-E input voltage, the positive B-To-E input voltage,, The collector current flows out of the C terminal; for negative voltage, the setting electrode current flows into the C terminal; 2) Public transmission polar amplifier works in non -counter -phase mode, while the public base is in the anti -phase mode; Far higher than bipolar transistors; 4) cross -guidance can be adjusted through external resistors; 5) Due to PTAT partial pressure characteristics, static current increases, such as changes in temperature shown by typical performance curves, and keep AC performance constant; 6) OTA is the sincePolarized bipolarity; 7) During the zero -difference input voltage, the output current is about zero. Angle -centered AC input generates zero -centered output current.

Basic application circuits

Most of the application circuits used in the OTA part consist of some basic types. These types have obtained the best understanding through analog discrete transistor circuit. Just as the crystal tube has three basic working modes: the total launch pole, the public base, and the public set electrode, OTA also has three equivalent working modes: Comm Mon-E, Common-B and Common-C (see Figure 36, Figure 37, 37 And Figure 38). Figure 36 shows an OTA connected as a public transmitted polar transistor amplifier. Input and output can be grounded without any partial pressure. The amplifier is irreversible, because the current from the transmitting pole flows also flows out of the collector, which is the result of the current mirror shown in Figure 35.

FIG. 37 shows a public C amplifier. It constitutes an open ring buffer with a low -dimensional voltage. Its gain is about 1 and changes with the load.

FIG. 38 shows a public B amplifier. This configuration generates a reverse gain, and the input is low impedance. When a high impedance input is required, it can be created by inserting a buffer amplifier (such as BUF602) by series.

Sample comparator

OPA615 sampling comparator has a very short switch (2.5ns) transmission delay, and adopts a new switch circuit structure To obtain excellent speed and accuracy.

It provides high impedance inverter and non -inverse simulation input, high impedance current source output and TTLCOMOS compatible control input.

The sampling comparator consists of a cross -guidance amplifier (OTA), a buffer amplifier, and a follow -up switch circuit. This combination was subsequently called a sampling operation cross -guidance amplifier (SOTA). The OTA buffer is directly connected to the buffer output end to provide two identical high impedance input and high -opening cross -conductor. Even a small differential input voltage is multiplied by high cross -direction, which will cause the output current to be positive or negative, depending on the input polarity. This characteristic is similar to the low or high state of the traditional comparator. The output of this current source has the characteristics of high output impedance, output bias current compensation, and optimizes the charging of DC recovery, nan seconds, peak detectors, and capacitors in S/H circuits. The typical comparator output current is ± 5mA. In the sampling mode, the output bias current minimizes to the typical ± 10 μA.

This innovative circuit realizes the high conversion rate representing the opening of the ring design. In addition, the collection and conversion current of maintaining or storage capacitors is higher than that of the standard diode bridge and switch configuration, eliminating the main factors of maximum sampling rates and input frequency limit.

The switch circuit in OPA615 uses current control (relative to the voltage switch) to improve the isolation between the switch and the simulation part. This design makes the aperture time of the analog input signal lower, which reduces the power supply and simulation switch noise. The sample injected by the peak switch charge is 40FC.

The additional offset voltage or switching transient of the capacitor at the capacitor at the capacitor at the capacitor output of the switch can be determined by the following formulas:

The switch -level input pair Keep the low conversion rate of control commands is not sensitive, and compatible with TTL/CMOS logic levels. In the case of high TTL logic, the comparator is in a state of activity, comparing the two input voltage and changing the output current accordingly. The logic of TTL is low, and the output of the comparator is closed, showing a very high impedance to keep the capacitor.

Application information

OPA615's working power supply is ± 5V (maximum ± 6.2V). The absolute maximum value is ± 6.5V. Do not try to operate under a large power supply voltage, otherwise it may cause permanent damage.

Basic connection

FIG. 39 shows the basic connection required for the operation. These connections are not displayed in subsequent circuits.

Power cross -road capacitors should be as close to the device pin as much as possible. Solid electric containers are usually the best. For further recommendations for the layout, see the Board Layout at the end of the application.

DC recovery system

Use Figure 615 and Figure 41 to restore two systems. FIG. 41 realizes the DC recovery function of a unit gain amplifier. From its name, it can be expected that this DC recovery circuit does not provide any amplification.

In applications that need to be enlarged, consider using the circuit design shown in Figure 40.

In order to make any normal work in these two circuits, the source impedance requires a very low, such as a closed loop large or buffer zone. Consider the video input signal shown in FIG. 42 and the complete DC recovery system shown in FIG. 40. This signal is large in OTA segment of OPA615, and the gain is:

DC recovery time. The sampling part of the signal is compared with the non -counter -phase input end of the SOTA (pin 10) or the reference voltage appearing on the ground in Figure 40.

When SOTA is sampled, it charges or discharge Chold capacitors based on the output signal level of the sampling. The appropriate regular details are shown in Figure 43.

Piece Video/RF amplifier

FIG. 44 shows another circuit example of the front amplifier and clamp circuit. The front amplifier uses a broadband low noise OPA656, which is also configured with+2V/v gain. Here, the typical bandwidth of OPA656 is 200MHz, the stable time is about 21NS (0.02%), and it provides low bias current JFET input level.

Video signals are blocked by capacitor CB to block DC components. In order to restore the DC level to the required baseline and use OPA615. Reverse input (pin 11) connect to the reference voltage. At the high time of clamping pulse, the switch comparator (SOTA) will compare the output and reference level of comparative amplifiers. Any voltage difference between these feet will cause the output current to charge or discharge the capacitor Chold. This charge generates a voltage on the capacitor, and the voltage will be generated by the OTA's collector C terminal through cross -guidance. This current will make the OPA656 level offset to its output voltage equal to the point of reference voltage. This level conversion will also turn off the control loop. Due to the buffer area, keep the baseline correction when the voltage of CHOLD is kept through the voltage of CHOLD.

External capacitors (Chold) have extensive flexibility. By selecting a smaller value, the circuit can be optimized within a short clamping cycle, or uses a high value at a low downturn. Another advantage of the circuit is that the peak of the small clamp at the output of the switch comparator is integrated and will not cause failure in the signal path.

The sampling maintenance amplifier

The control transmission delay of OPA615 is 2.5ns and the bandwidth is 730MHz. It can be used for high -speed sampling maintenance amplifiers. Figure 45 illustrates this configuration.

In order to explain how to digitize in the circuit in Figure 45, Figure 46 shows 100kHz sine waves sampled at a rate of 1MHz. The output signal used here is the iOUT output that drives 50 load.

NS pulse accumulation

Use the NS pulse accumulation of OPA615 (as shown in Figure 47) to output the fast comparator and its current mode. Highly control control, narrow pulse charging capacitor to increase the average output voltage. In order to minimize the ripples input input and maximize capacitor charge, the T network is used in the feedback path.

The Pulse Peak Value Values u200bu200b

can design a circuit similar to FIG. 47 (ns pulse integror) And negative pulse. As shown in Figure 48, the circuit uses OPA615 and BUF602. This circuit profitUse a diode to isolate the positive pulse to the negative pulse and charge different capacitors.

The fast -locking ring phase detector

FIG. 49 shows the circuit used for the phase detector for the fast -locking ring system. As a reference pulse, the comparator is used as a reference pulse in this pulse string. This voltage is then buffered by OTA and sent to VCO.

Related dual sampling device

Noise is a limit factor for the resolution of the CCD system, where KT/C noise accounts for dominant position (see Figure 51). To reduce this noise, the imaging system uses a circuit called the relevant dual sampling (CDS). Its name comes from the dual sampling technology of the CCD charge signal. Use two OPA615s and an OPA694 CDS as shown in Figure 50. The first sample (S1) was collected at the end of the reset cycle. When the reset switch is turned on again, the effective noise band is changed due to the large differences between the switch RON and the ROFF resistance. This difference causes the main KT/C noise basically to freeze at the last point.

Another sample (S2) was performed during the video part of the signal. Ideally, the difference between the two samples is only to the voltage of the transmission of charge signals. This is a video electricity leveling noise (u0026#8710; v).

The CDS function will eliminate KT/C noise and most 1/f and white noise.

FIG. 52 is the frame diagram of the CDS circuit. Two samples keep the amplifier and a differential amplifier constitute a related dual sampling device.

The signal from CCD is applied to these two samples to keep the amplifier, and its output is connected to the differential amplifier. The time sequential map clarifies the operation (see Figure 52). At the time of T1, the sampling maintenance (S/H1) enters the maintenance mode, and samples the reset level, including noise. The voltage (VRESET) is applied to the non -reversing input of a differential amplifier. At time T2, the sampling maintenance (S/H2) will sample the video level, that is, VRESET -VVIDEO. The output voltage of the differential amplifier is vout u003d vin+--vin-. The reset voltage sample contains KT/C noise, which is eliminated by the subtraction of the differential amplifier.

Dual sampling technology has also reduced white noise. White noise is part of the reset voltage (VRESET) and VRESET -VVIDEO. Assuming that the noise of the second sample is not changed from the noise of the first sample, the noise magnification is the same as the latitude, and it is related to time. Therefore, the CDS function can reduce noise.

Circuit plate layout guide

To get the best performance and high -frequency amplifier like O o.PA615 needs to pay close attention to the layout parasites and external component types of printing circuit board (PCB). Suggestions for optimization include:

A) Putting all signal input/output pins to the minimum parasitic capacitor to any communication to the minimum. Parasitic capacitors at the output terminal and inverter input terminals will cause unstable; at non -inverter inputs, parasitic capacitors will react with the source impedance, resulting in unintentional bandwidth limit. In order to reduce unnecessary capacitors, a window should be opened on all the ground and power plane around the signal I/O pins. Otherwise, the ground and power aircraft should remain complete elsewhere.

B) The distance between the power pins and the high frequency 0.1 μF decoupling capacitor (u0026 lt; 0.25 "") minimizes. At the device pin, the ground layout of the grounding and power supply should not be close to the signal input near the signal input /Output pin. Avoid narrow power and ground traces to minimize the inductance between the pin and the decoupling capacitor. The power connection should always be disconnected with these capacitors. Used for bipolar operations) will improve the second harmonic distortion performance. The main power supply should also use larger (2.2 μF to 6.8 μF) decoupling capacitors, which is valid at a lower frequency. Far places, and can be shared between multiple devices in the same area of u200bu200bPCB. C) Careful selection and placing external components will maintain the high -frequency performance of OPA615. The resistor should be very low electric resistance. Type. Surface stickers are the best work and allow more compact overall layouts. Metal membrane and carbon composition, axial binding resistance can also provide good high -frequency performances. Once again, these leading and PCB tracking lengths are as short as possible as possible as possible as possible as possible as possible as possible. . Do not use a wire -winding resistor in high -frequency applications. Other network components, such as non -converting input terminal connecting resistors, should also be placed near the package.

d) and other broad band equipment on the board on the board The connection can be performed through a short direct record or through the plate transmission line. For short connections, the input of the next device is considered as a concentrated capacitor load. It is best to turn on the ground and power aircraft around it.

E) It is not recommended to put high -speed parts like OPA615 in. The additional lead length of the socket and the capacitor between the tube will produce a very troublesome parasitic network, almost almost almost It is impossible to achieve a smooth and stable frequency response. OPA615 can be directly welded to the PCB to get the best effect.

ESD protection

OPA615 is a very high -speed, complex bipolar craftsmanship. Made in. For these very small geometric devices, the internal knotting voltage is relatively low. These faults are reflected in the absolute maximum rated table, which reports the absolute maximum ± 6.5V power supply. All device pins have limited ESD ESDs Protection, use the Internet diode power supply, as shown in Figure 53.

These diode also provides moderate protection to input over -drive voltage higher than the power supply.Protecting diode can usually support 30mA continuous current.If there may be a higher current (for example, in a system that drives to OPA615 with ± 15V power components), adding a string -limited connected resistor should be added to two input terminals.These resistance values are as low as possible because high value will reduce noise performance and frequency response.