An operational amplifier is a typical analog integrated circuit. It can be said that there is an analog integrated circuit with an operational amplifier, and its history is the history of analog integrated circuits. The design and development of operational amplifiers is not as intuitive as its external characteristics; the huge internal differences of operational amplifiers with subtle differences in external characteristics are often unexpected; resources invested in the development of operational amplifiers with subtle differences are engineering requirements and engineering requirements. the pursuit of commercial interests and the need for intellectual property innovation. The clues can be seen from the product development of Shengbang Microelectronics in recent years.
Micropower Operational Amplifier
Dramatically reducing power consumption has more than an impact on application design than energy savings. If the average power needs to drop from the order of mA to the order of μA or even below, the power supply scheme can be very different, enabling some applications that would otherwise be inconvenient and impossible to achieve. For example, the power supply circuit shown in Figure 1 can drive a circuit with a micro-power operational amplifier as the detection part, cooperate with energy storage and intermittent execution part, and use a single power line to control the load. Some power switch boxes are actually just a line. Upgrading these switches, such as upgrading to remote dimming or proximity switches, requires powering the control circuit. When the load is not turned on, power is supplied by allowing a small amount of current to flow. If this current is large, it will cause partial start-up or intermittent start-up of the load; especially for light loads, such as 3~5W LED lamps. The actual engineering case solves this problem by using the micro-power consumption characteristics of SGM8041.
Figure 1. Schematic diagram of changing the power supply circuit with a micro-power op amp
The circuit shown in Figure 1 is designed to work within the voltage range of alternating current, but only R (and between the actuator and the primary and secondary sides of the current transformer T) of its components bears a higher voltage, and the withstand voltage of the rest of the components is based on reference The breakdown voltage of the Zener is used as a reference. The current transformer T is used in the application of large power load to supply power to the control circuit during the on-time; if the load is small, a certain voltage difference can also be obtained by delaying the opening angle during the on-time to supply power to the control circuit. Figure 1. Schematic diagram of changing the power supply circuit using a micropower op amp.
Low-power products have become very popular, such as the commonly used TLC27L and MCP6041; the latter quiescent current is only 600nA. SGM8141/2 is a more extreme micro-power computing product, its quiescent current is only 350nA, and Voffset is controlled within a maximum of 2.5mV. Using the SGM8141/2 can provide continuous parameter monitoring when the system is in deep sleep for wake-up or abnormal triggering. Also used in designs that are self-powered by signals or that utilize energy harvesting such as vibration, heat, and light.
Figure 2. Offset voltage distribution of Shengbang micropower op amp
The challenge in micropower op amp design is to maintain a small and stable offset voltage over the full input range with as little circuitry as possible. Micro-power op amps cannot use complex circuits to compensate for temperature changes and lock the bias of the input section strictly according to the common mode. Offset compensation relies on parameter compensation design and fine layout design. Figure 2 is the offset voltage distribution statistics of Shengbang’s micro-power op amp products.
The comparator is an analog integrated circuit that is normally in a quasi-saturation state, and only behaves linearly in a small interval near the comparison threshold. The need for comparators is often overlooked and misunderstood in both high-speed and low-speed applications. In reality, there are many successful engineering cases of using amplifiers as comparators, which truly reflect the changes in the demand for comparators. The comparator is different from the operational amplifier in terms of parameter optimization and actual structure implementation; the transmission gain of the comparator before or after the output inversion is small to prevent self-excitation; the rising or falling edge after triggering the inversion is not affected by the ramp rate of the previous stage Impact. Most of the needs of comparators in traditional engineering have been replaced or weakened, such as quickly crossing the logic fuzzy area of logic devices, accurate amplitude discrimination, and suppressing the indeterminate state output near the discrimination threshold.Mainly because of the popular use of ADCs and the improvement of logic I/O design; whether in logic I/O circuits or using the mild positive feedback hysteresis of op amps, logic uncertainty can be effectively avoided, and the timing jitter characteristics have always been Not a Comparator’s forte1.
Shengbang’s design improvement focuses on reducing the power consumption of the comparator. When the micro-power op amp is used as a comparator, the operating current in the saturation state increases, and it takes a long time to exit saturation, but the comparator does not have these problems. Referring to Figure 3, the operating current of the SGM8701 series micro-power is stable at a very low level around 300nA.
Figure 3. SGM8701 Series Comparator Operating Current
Very low-power comparators can be used in applications that require a latent or deep sleep state, such as continuous monitoring of battery voltage during standby and continuous monitoring for wake-up calls. Figure 3. SGM8701 series comparator operating current.
No Crossover Distortion Operational Amplifier
Different from the crossover distortion concept of BTL and Class C amplifiers, the crossover distortion-free op amp is proposed relative to the full-scale input CMOS op amp with input structure-dependent crossover distortion. CMOS operational amplifiers have outstanding advantages such as high input impedance, low operating current, easy to achieve full-scale output, and no need to distinguish between single and dual power supply designs, but their input part requires a large voltage difference between the gate and the source, and the common-mode input voltage The small range limits the use of low operating voltages. The complementary double differential pair structure shown in Figure 4 is used in CMOS op amps to allow rail-to-rail inputs. This complementary dual differential pair structure ensures that at least one differential pair will work regardless of whether the common-mode voltage is close to the positive supply or close to the negative supply. Engineering reality cannot guarantee that the two differential pairs will have exactly the same offset voltage. Changes in the input common-mode voltage cause the complementary dual differential pairs to alternate operation causing input-dependent crossover distortion.
Figure 4. Complementary double differential pair input structure causing crossover distortion.
Unlike the crossover distortion caused by the output alternation of the output totem-pole structure, the input-dependent crossover distortion cannot be improved by increasing the open-loop gain. SGM8942 avoids the use of dual complementary differential pair structure by changing the bias structure of the input part, and is a new type of full-scale input/output operational amplifier without crossover distortion.
Input-dependent crossover distortion occurs only in non-inverting amplification applications such as electret output buffering of amplifiers requiring high input impedance, output buffering of piezoelectric transducers, buffering of PT/CT gas sensor outputs, and potentiometer output buffering. Crossover distortion produces spurious spectra, or spurious perturbations. The SGM8942 is successfully used in perturbation-sensitive applications such as micro-arc detection, instantaneous power factor measurement, and electrochemical diffusion potential detection.
High Precision Operational Amplifier
From the perspective of intrinsic characteristics, CMOSFET’s stability and noise characteristics, especially 1/f noise, and response speed are not as good as bipolar transistors; but its advantages of high input impedance, low bias current, low power consumption and compact structure Bipolar devices are hard to come by. Since the advent of CMOS products, efforts to improve their noise, stability and speed have never been interrupted. Except for a few special applications, CMOS op amps have replaced bipolar op amps as the main force. For example, the SGM8551 series of high-precision op amps can guarantee an offset voltage of less than 20μV and a temperature drift of less than 20nV/°C, surpassing traditional high-precision op amps such as OP07 and the similar LMV2011 in all aspects. SGM8551 has been successfully used in 6 and a half precision process calibration instruments.
The significance of high-precision operational amplifiers to application engineering is clear and need not be repeated, but its design engineering challenges are quite special; high-precision operational amplifier design is a patent-intensive field, and many circuit schemes and wiring schemes are protected; new designs must be protected and Innovation under the principle of utilization. Shengbang’s high-precision op amp product design is a combination of the industry’s latest data models and some innovations.
Different from the flexible and changeable scheme in the high-precision measurement amplification system, such as the correlated double sampling scheme2chopper modulation amplification scheme3and chopper tracking scheme4And so on, the realization scheme of high-precision operational amplifier is limited to two basic schemes of precision tracking compensation and alternating auto-zero.
Referring to Figure 5, the principle of the alternating auto-zero scheme is similar to that of a chopper tracking amplifier. The first stage on the signal channel is divided into two groups with exactly the same geometric distribution; except for the moment of switching, there is always one group passing the signal, which ensures that the signal is transmitted and amplified approximately continuously; the auto-zero calibration is alternately ongoing. The offset of a group that is not passing the signal is fed into the nulling channel, and the offset is adjusted to make the offset zero.
Figure 5. A schematic illustration of the principle of alternating auto-zero.
High Voltage Operational Amplifier
In industrial sites or similar harsh conditions, the use of op amps that can directly work at higher voltages is beneficial to improve availability and lameness.5. Just increasing the operating voltage has limited improvement in design tolerance; in fact most early bipolar op amps can operate at higher voltages, but not at lower voltages. The high adaptability required for high voltage op amps in the modern sense includes a large dynamic operating voltage range, rail-to-rail input/output, immunity to high common mode/differential mode, and short-term overvoltage tolerance. Taking SGM8291 as an example, its operating voltage range is 4.5V~36V, both common mode and differential mode input are allowed to the power supply voltage, and the short-term overvoltage of the power supply can exceed 40V.
The high-voltage op amp in the modern sense is a relatively new type of op amp. For example, TI has only recently begun to promote its OPA171 series of high-voltage op amps. All of these high-voltage op amps have the characteristics of large dynamics and low current. They use JFET or CMOS as input, and generally adopt a BCD hybrid structure; their characteristic advantages are that bipolar high-voltage op amps cannot resist analogies. The structure of high-voltage op amps is different from that of low-voltage op amps. For example, the input section has to maintain a stable offset voltage over a much larger common-mode voltage range, and the output section has to withstand a large gate-drain (or base-collector) voltage. The SGM8291 has an offset of no more than 0.9mV over the full voltage range and allows the output to be shorted for long periods of time.
Figure 6 is used to explain a schematic scheme of how to implement the structural differences required for these features (this schematic does not imply that Shengbang uses this structure). Among them, CC1~CC3 constant current sources need to use bipolar intrinsic constant current characteristics to stabilize the bias of the input differential pair; A uses CMOS to achieve high gain; T1 and T2 use DMOS to achieve high withstand voltage. Low voltage op amps do not need these combinations.
Figure 6. Schematic explaining the differences in high voltage op amp construction.
The social significance of developing high-voltage op amps and improving the industrial product chain is greater than the direct economic significance of developers, and it is the embodiment of Shengbang’s strength and self-confidence. Although high-voltage op amps are indispensable for industrial applications, their application space is constantly crowded by low-voltage structural systems.One is that in most systems, the signal is ultimately fed to or initially from a low-voltage digital processing circuit, and low-voltage systems already have high system-level design tolerances; the other is that peripheral circuit improvements can use low-voltage circuits to achieve tolerances similar to high-voltage devices.6, share the dividends of low-voltage components with large selectivity, good supply and low prices. However, some application scenarios are destined to require high-voltage op amps. Figure 7 illustrates several situations where high-voltage op amps are suitable for use on the input and output sides.
Figure 7. Several situations where a high voltage op amp is required.
Field yellow flowers are particularly fragrant
semiconductor integrated operational amplifiers have been developed and marketed since the 1960s. After half a century of vicissitudes, new products can still be seen today.1, witnessed the continuous pursuit of human beings to deeply explore and improve themselves. In recent years, several new semiconductor companies have emerged in China, like Shengbang, whose main business is the development and promotion of analog integrated circuits, making contributions to expanding applications and promoting market competition; the characteristics and characteristics of Shengbang’s products introduced in this article are all Already on par with known high-performance products. In mature applications, analog circuits including op amps are increasingly integrated into single-chip systems. At the same time, with the deepening of understanding and the strengthening of processing capabilities, there are constantly new requirements that require new products to meet . New products and being integrated, surpassed and surpassed are the same progress, development and continuation.
Thanks to Dr. Shilong Zhang, CEO of Shengbang, for his review and permission to talk about the company’s new products and their important applications. Dr. Yao Ruoya, a senior application expert of Shengbang, also reviewed the full text of this article and provided important opinions on the elaboration of low-power applications.
1 Locally linear limiting amplifiers have the best deterministic jitter characteristics. In addition to the deterministic jitter caused by the two stages itself, the comparator pre-stage with built-in hysteresis causes additional jitter, and the jitter without hysteresis is more related to the rate of change of the input signal.
2 is to collect two data related to noise/interference and different signals in time or space, and use the relevant part of the data to eliminate the noise/interference.
3. The low-frequency signal is converted into a high-frequency signal in a specific frequency range by chopper modulation, and after filtering and amplifying, the high-frequency signal is measured, and the measurement scheme is reversed to the modulated low-frequency signal.
4. Use the measurement method that switches the phase of the signal and the phase of the amplification channel at the same time, so that the signal remains unphase-commutated, and the interference and noise are cancelled by the phase-change.
5. Availability is the ratio of the time that the equipment can maintain effective operation; lameness is the ability to maintain a certain work even when the working conditions are partially lost, which is related to the design tolerance of the system.
6 For example, the use of voltage divider and power supply protection bootstrap float, can withstand high voltage and withstand short-term overvoltage.