This application note introduces the use of the CDBCAPTURE system and the embedded A/D converter. This article will introduce the CDBCAPTURE system and give some examples.

This application note introduces the use of the CDBCAPTURE system and the embedded A/D converter. This article will introduce the CDBCAPTURE system and give some examples.

The CDBCAPTURE system can be used to collect data from an embedded analog-to-digital converter (ADC). Therefore, the system performance of the analog front end can be measured, analyzed and quantified. By analyzing the measured performance, the noise source can be identified, isolated, and corrective actions can be taken. Here CDBCAPTURE is used as an engineering tool to reduce development time during system testing and integration. Another application may be to use CDBCAPTURE in production to test finished products and verify system performance.

CDBCAPTURE

The CAPTURE interface board is a development tool for connecting the Crystal semiconductor ADC to a PC compatible computer. The digital data from the ADC is collected in a high-speed digital FIFO, and then transmitted to the PC through the serial COM port. Includes evaluation software to analyze data and demonstrate ADC performance. The whole system is composed of CAPTURE interface board, serial cable, RS232 cable and software.

CDBCAPTURE with embedded ADC

The CDBCAPTURE board is designed to interface directly with most Crystal Semiconductor ADC evaluation boards. This provides a quick and easy way to quantify and verify ADC performance. However, it is usually necessary to measure the performance of the ADC in the actual system or to measure the overall system performance. To collect data from the embedded ADC, a special serial cable needs to be designed. This cable contains the digital interface circuit present on the evaluation board. This cable is connected to the corresponding signal on the ADC.

To collect data from the embedded ADC, the digital interface circuit on the evaluation board needs to be integrated on the modified serial cable. Figure 1 is a block diagram illustrating this process. At the top of Figure 1, the evaluation board CDBXXXX contains a digital interface circuit that converts the signal from the ADC into three standard serial signals, namely FRAME, SCLK, and SDATA. The timing and format of these signals vary by device type.

About the use of CDBCAPTURE system and embedded A/D converter
CDBCAPTURE interface

In embedded ADC applications, the digital interface circuit between ADC and CDBCPATURE circuit card should be implemented on a small card connected to the serial cable, as shown at the bottom of Figure 1. Need to identify the appropriate digital input signals. Then implement the method of connecting these signals from the embedded system to the cable. The connection scheme varies from application to application and is easy to implement.

The schematic diagram of the digital interface circuit is provided in the evaluation board data sheet. Locate the serial interface connector on the schematic that contains the following signals: +5 V, GND, FRAME, SCLK, and SDATA. Start working from this connector and go back to the ADC to determine the circuitry required to create the serial signal. The circuit is implemented on a separate circuit board, connected to a 10-core ribbon cable, with an IDC socket for its CDBCAPTURE interface. The ADC interface can be any connector scheme that is easy to implement. Possible alternatives include pile heads, test clips, circular connectors or “D” type connectors.

CS5508 example

The following example uses CS5508 to illustrate the process of designing a modified serial cable. By checking the schematic diagram of the CDB5508 evaluation board, the digital interface circuit can be determined. The schematic diagram of the CDB5508 evaluation board is provided in Figure 1 of the CDB5505/6/7/8 data sheet. The digital interface part is shown in Figure 2 below. If CS is always active, resistors R23, R24 and R25 are not needed. In addition, when using the CAPTURE board, U3B is always active, so it can be changed to a general buffer, such as U2.

About the use of CDBCAPTURE system and embedded A/D converter
CDB5508 Digital Interface Evaluation Board Schematic Diagram

Figure 3 shows the schematic of the modified cable from Figure 2. The DRDY, SCLK, and SDATA signals are buffered to create the serial cable signal for the CAPTURE board. The 5 volt power is obtained from the embedded system and filtered by R1 and C1 before being provided to the CAPTURE board. C2 is the bypass capacitor of U1.

About the use of CDBCAPTURE system and embedded A/D converter
Modified serial cable realization of digital interface

The CDBCAPTURE system is designed to easily connect to most Crystal Semiconductor ADC evaluation boards. The evaluation board contains digital circuits to implement a standard serial data bus. The CAPTURE board can be reconfigured through software to adapt to different ADCs and future products. The CDBCAPTURE system allows easy transmission of digital data to a PC for analysis.

Many times, when the ADC is running in a complete acquisition system, it is desirable to collect data from the ADC. In this case, the digital interface circuit of the CAPTURE board is realized by a modified cable outside the system. The electrical system must provide an appropriate interconnection scheme, using connectors or test points to clamp on it.

The modified serial cable allows the user to measure the performance of the ADC while it is embedded in the electrical system. The ADC and system performance can be measured and quantified. This information is used to isolate problems and investigate how certain subsystems interact with each other.

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