How to deal with bugs in amplifier circuit design

Modern integrated operational amplifiers (op-amps) and instrumentation amplifiers (in-amps) bring numerous advantages to design engineers when compared to discrete components. Despite their many clever features and functionalities, there are often overlooked issues that can lead to circuit malfunctions. These problems might not surface immediately during testing but can cause unexpected behavior over time, particularly in critical applications. This article aims to address some of the most common pitfalls encountered in practical applications and provide practical solutions. One of the most frequent challenges arises from the lack of a DC bias current loop in AC-coupled op-amp or in-amp circuits. Referring to Figure 1, placing a capacitor in series with the non-inverting input of an op-amp is a straightforward way to block DC components from the input voltage (VIN). This technique is especially valuable in high-gain applications, where even minor DC offsets could restrict the dynamic range or trigger output saturation. However, neglecting to provide a path for the bias current to flow through the high-impedance input can create significant issues. In such scenarios, the input bias current charges the coupled capacitor until it exceeds the common-mode voltage limits of the amplifier, causing the circuit to malfunction. Depending on the polarity of the bias current, the capacitor may charge to either the positive or negative rail voltage. The closed-loop DC gain of the amplifier then amplifies this bias voltage, leading to output drift. For instance, with a FET-input amplifier having a bias current of 1 pA and a 0.1 μF capacitor, the charging rate would be 10 μV/s, resulting in a 600 μV drift every minute. While this might seem negligible during initial lab tests, the cumulative effect becomes apparent after hours of operation, causing erratic behavior or complete failure. To resolve this issue, a simple yet effective solution involves adding a resistor between the input and ground to establish a DC path for the bias current. Figure 2 demonstrates this approach in a dual-supply op-amp configuration. By ensuring the resistance of R1 equals the parallel resistance of R2 and R3, the offset voltage caused by the input bias current can be minimized. Typically, resistor values range from 100 kΩ to 1 MΩ, balancing the need for low noise against maintaining adequate circuit impedance. Similar challenges arise in in-amp circuits, particularly when AC coupling is employed without providing a return path for the input bias current. Figures 3a and 3b illustrate common mistakes in dual- and single-supply configurations. These issues can also manifest in transformer-coupled amplifier circuits, as shown in Figure 4, where the secondary coil lacks a proper DC-to-ground loop. Figures 5 and 6 present practical solutions for addressing these problems. In dual-supply in-amp circuits, connecting high-value resistors (RA and RB) between each input and ground provides a discharge path for the bias current. In single-supply setups, the reference terminals of the inputs can be grounded or connected to a bias voltage, often set to half the maximum input voltage. Applying the same principles to transformer-coupled circuits ensures stable performance. When dealing with instrumentation amplifiers, properly configuring the reference voltage is equally critical. Many design engineers mistakenly assume the reference input is high impedance and attempt to drive it directly with a resistor divider. However, this approach can degrade performance in certain instrumentation amplifiers, as illustrated in Figure 8. For example, a popular design using a three-op-amp architecture suffers from altered symmetry and reduced common-mode rejection when the reference input is sourced incorrectly. Adding a buffer amplifier between the voltage divider and the reference input, as shown in Figure 9, resolves these issues while allowing for easy adjustments. Another frequently overlooked aspect is the impact of supply voltage variations on the circuit’s performance. Modern op-amps and in-amps offer impressive power supply rejection (PSR) capabilities, but they rely heavily on proper bypassing techniques to maintain stability. A simple yet effective solution involves adding a large capacitor to the voltage divider output, as depicted in Figure 10, to filter out supply fluctuations. This ensures consistent PSR performance, even under varying load conditions. Single-supply op-amp circuits require careful attention to decoupling the bias voltage, particularly when derived from a voltage divider. A common mistake involves using a 100 kΩ/100 kΩ resistor divider with minimal bypass capacitance, which often leads to instability, especially when driving inductive loads. Figures 12 and 13 demonstrate optimized decoupling schemes that maintain stability while ensuring proper biasing. By addressing these practical challenges, designers can ensure reliable and robust performance of their circuits. These considerations highlight the importance of thorough testing and thoughtful design practices, even in seemingly straightforward implementations.

WiFi 5 Wireless Router

First, Wireless Router
So what is a wireless router?

Wireless router, according to the definition of Baidu Encyclopedia: Wireless router is used for users to access the Internet, with wireless coverage of the router.

A wireless router can be thought of as a repeater that forwards the broadband network signal from the wall of your home through an antenna to nearby wireless network devices (laptops, Wifi-enabled phones, tablets, and all Wifi-enabled devices).

The popular wireless routers in the market generally support four access methods: dedicated xdsl/cable, dynamic xdsl, pptp, and generally can only support 15 to 20 devices online at the same time. It also has some other network management functions, such as dhcp service, nat firewall, mac address filtering, dynamic domain name and so on. The signal range of the general wireless router is 50 meters radius, and the signal range of some wireless routers has reached 300 meters radius.

The name of wireless router can be separated out of two keywords: wireless and routing.

Understand the technical principle behind these two words, you understand the wireless router.

Wireless is also what we often call Wi-Fi. Wireless routers can convert home broadband from wired to wireless signals, and all devices can happily surf the Internet as long as they connect to their own Wi-Fi. In addition, these devices also form a wireless local area network, where local data is exchanged at high speed and is not limited by the bandwidth of home broadband.

For example, many people have smart speakers in their homes that can be used to control various smart appliances. When you say small X small X, turn on the TV, the speaker actually finds the TV through the LAN and sends instructions, and does not need to connect to the Internet; And if you let it broadcast news, you have to get data through the Internet.

The Local Area Network we talked about earlier, also known as the Intranet, is represented by the Local Area Network (LAN) on the router, so the Wi-Fi signal is also called WLAN(Wireless LAN); The Internet we want to access, also known as the extranet, is represented on the router by the WAN(Wide Area Network).

On the Intranet, the IP address of each device is different, which is called a private address. All devices on the Internet share the same public address, which is assigned by broadband operators such as China Telecom Unicom.

The router is the bridge between the Intranet and the external network. The above mentioned IP address translation, packet forwarding, is the router routing function. In other words, the router is the hub of the home network, and the data of all the devices must be forwarded through it to access each other or reach the external network, which means that one husband is the key and ten thousand men are not open, so the comprehensive router is also called "home gateway".

Second, the demand for wireless routers
I do not know if there is a sudden WIFI break when you play games at home, and a stable router is crucial at this time. However, it is important to note that your WIFI frequently dropped may not be a problem with the router, it may also be a problem with the carrier network. (Router means I don't back this pot)

In fact, for most people, there are two basic requirements for wireless routers

Stable and do not drop
Fast Internet and easy setup
Some people will have some advanced needs:

There are some features, USB interface, can be external U disk or hard disk, can achieve simple nas functions, QOS, etc., to advertising and so on
Mesh networking, when the house area is large, multiple routers can be used for Mesh networking

How to choose a wireless router
The wireless router market is in the transition stage from WiFi 5 to WiFi 6, if you want to buy the first choice is definitely WiFi 6 wireless router, which is the future trend.

The speed of WiFi 6 is nearly 40% higher than the previous generation 802.11ac, and the highest connection speed can even reach 9.6Gbps, while the highest speed of 802.11ac is only 6.93Gbp. More importantly, unlike 802.11ac, which only covers the 5GHz band, WiFi 6 covers 2.4GHz and 5GHz. Although the 5GHz band has less interference, it has weak wall penetration ability, and the 2.4GHz band has strong wall penetration ability, which takes into account each other.

So why choose a WIFI6 router?

Compared with the previous generation of 802.11ac WiFi 5, the maximum transmission rate of WiFi 6 in the 5Ghz band has been increased from 3.5Gbps to 9.6Gbps, and the theoretical speed has been increased by nearly 3 times. WiFi 6's 5Ghz single-stream 80Mhz bandwidth can reach theoretical speeds of up to 1201Mbps and 160Mhz bandwidth of up to 2402Mbps.
The band supports 2.4Ghz and 5Ghz.
In terms of modulation mode, WiFi6 supports 1024-QAM, which is higher than the 256-QAM of WiFi 5, and the data capacity is higher. Some high-end WiFi 6 routers support 4096-QAM.
WiFi6 supports MU-MIMO (multi-user multiple-input multiple-output) technology, and supports both upstream and downstream MU-MIMO, with a maximum support of 8T×8R MU-MIMO. The speed is greatly improved. High concurrency, WiFi6 5GHz band, terminal connections up to 128! 5 times that of WiFi5. Effectively solve the Internet needs of multi-person networking and smart home;
WiFi6 adopts OFDMA (orthogonal frequency division multiple access) technology. After using OFDM to parent the channel, the transmission technology of transmitting data is loaded on the subcarrier, allowing different users to share the same channel, allowing more devices to access, with shorter response time and lower delay.
Low latency, WiFi6 time delay can be as low as 10ms, compared to WiFi5 30ms delay, only 1/3. This performance refresh is extremely friendly to game lovers;
If WiFi6 (wireless router) devices need to be certified by the WiFi Alliance, they must use the WPA 3 security protocol, which is more secure.
The WiFi6 wireless router is backward compatible with WiFi5 and WiFi4 terminals.

Fourth, the misunderstanding of purchasing routers
Is the through-wall router really through-wall?
Mistake; The country has strict limits on the transmission power of the wireless router antenna, if you have a lot of rooms in your home, and there are many walls between them, even if you buy an expensive wireless router, you can not do one to cover all the room signals. If the signal is not good, you can consider multiple wireless router Mesh networking.

Does a wireless router have a stronger signal with more antennas?
More antennas just to match the X*X MIMO mode, the more antennas, the more channels, can only ensure that the network is more stable, the impact on the signal is little, the strength of the signal is only related to the wireless transmission power. The wireless transmission power of the country has a standard.

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Shenzhen MovingComm Technology Co., Ltd. , https://www.movingcommtech.com