At the same time, high DC accuracy and high bandwidth are required, which may be difficult to implement. We can provide several effective methods depending on the circuit configuration, including building a composite amplifier or implementing a servo loop based on a high speed amplifier.
For an inverting circuit configuration, it is best to implement a DC servo loop that uses an operational amplifier (configured as an integrator). For a normal phase circuit, the easiest way is to implement a DC servo loop based on an operational transconductance amplifier (OTA). The two circuit views are shown in Figure 1 and Figure 2, respectively.
Figure 1: DC servo loop in an inverting amplifier configuration
Figure 2: DC servo loop for a positive-phase amplifier configuration
Both circuits are AC coupled circuits, whether or not the user wishes to use a tantalum capacitor. I am talking about a circuit that supports decoupling capacitors to emphasize that the equivalent circuit is AC coupled.
An effective servo loop removes the DC voltage and can be replaced with a reference voltage (Vref). System accuracy is limited only by the accuracy of the devices used in the servo loop and the loop speed. In both circuits, the user must balance the high-pass bandwidth with the servo amplifier response time. If the servo amplifier is too fast or the signal changes too slowly, the servoed signal will be affected by severe signal integrity. In addition, the system will provide initial setup time before accurate measurements are achieved.
For integrator-based circuits, the servo amplifier output voltage increase is closely related to the signal amplifier output. Since the DC gain is 1-V/V, the input and output of the signal amplifier will then be equal. A low-pass filter consisting of R4 and C3 limits the bandwidth and minimizes the noise introduced to the signal amplifier. The servo amplifier is usually a precision amplifier such as the OPA277 or OPA333.
The positive-phase configuration of the DC servo loop is identical to the integrator and supports up to the output of the OPA615 sampled OTA (SOTA). The voltage difference between pins 10 and 11 will generate a current output that will charge the Chold capacitor. The resulting voltage will then be fed to another OTA. The voltage present at the OTA B input (Pin 3) can be mirrored to the E input as a voltage and converted to current through the resistor RE. This current is ultimately mirrored to the C output (pin 12) and inserted into the inverting node of the OPA656. The current continues to increase to this node until the voltage difference across pins 10 and 11 is zero.
For some of the more complex circuits, SOTA can be used to sample a specific time during which no signal reaches a certain DC value, actually shifting the entire signal up and down. In this mode, the circuit will function as a DC recovery circuit. If the SOTA is always sampling, DC correction can only be achieved by inserting an RC filter on pin 10. This RC filter works the same as the R4C3 filter in Figure 1.
CCTV Power Supply,CCTV Power Supply Box,CCTV DC Distributed Power Box
Chinasky Electronics Co., Ltd. , https://www.cctv-products.com