This article introduces how to use advanced testing platforms to test certain key parameters of ADSL chips, so that semiconductor manufacturers can reduce the testing cost of ADSL devices.

ADSL is a modem technology that fully utilizes the unused resource capacity of ordinary telephone twisted pair cables. It adopts an asymmetric transmission method, and the downlink speed from the central office (CO) to the remote end (RT) can reach up to four times the uplink speed. This asymmetric performance is ideal for market oriented consumer broadband applications such as video and Internet access, because the downlink data rate must be very high in these applications, while the uplink data from users to the central office (CO) is generally small. This usage model is also applicable to business communication from company servers to employees, partners, and customers.

Unlike analog modems, ADSL modems do not enter the Public Switched Telephone Network (PSTN) and use advanced modulation technology, resulting in higher signal frequencies and data rates than analog modems. ADSL supports a maximum downlink speed of up to 8Mbps and an uplink speed of up to 832kbps. However, as the signal transmission distance increases, the data transmission rate using this technology will also quickly decrease. For example, when the distance between the user end and the office end is below 12000 feet, the ADSL speed can maintain 8Mbps, but when the distance increases to 18000 feet, its speed can only reach 1.5Mbps.

ADSL uses the familiar Frequency Division Multiplexing (FDM) method to provide broadband services, while also supporting traditional Standard Telephone Service (POTS) networks. The FDM method used in ADSL is mainly Discrete Multi tone (DMT) modulation. The DMT modulation method divides the approximately 1.1MHz spectrum into 256 equally spaced subchannels or tones, with each subchannel accounting for 5.3125KHz. In the DMT spectrum, each channel operates independently and uses orthogonal amplitude modulation (QAM) modulation method to encode digital information.

These channels can be used not only for data transmission, but also for independent network management or performance testing. Lower frequency channels are not used for signal transmission and are generally reserved as protective bandwidth to avoid interference with traditional POTS devices located at the lower end of the spectrum. In the frequency bands adjacent to and higher than these protected channels, a small number of channels are allocated for uplink data transmission, while the remaining higher frequency channels are used for downlink data transmission. Just like other modem technologies such as V.32 and V.34 modems, ADSL modems also need to use echo cancellation technology to solve the problem of overlapping uplink and downlink channels. To provide both telephone and data services simultaneously, it is necessary to rely on low-pass filters or separators to achieve separation.

test method

In order to improve the cost-effectiveness of ADSL, manufacturers need to provide equipment that can extend the distance between the central office and the user end, which can reduce the number of terminal points and thus lower the cost of laying fan-shaped user lines. In addition, the coverage performance of ADSL devices is the most competitive factor. A longer telephone line can cause up to 90dB attenuation to the high-end band signal used by ADSL. Therefore, semiconductor manufacturers typically use analog-to-digital converters (ADCs) and digital to analog converters (DACs) with higher dynamic range and lower noise indicators in the design of ADSL devices.

In ADSL modems, the noise and linear performance of YS1700-000A34 analog front-end (AFE) are key factors for ADSL modems to achieve ideal data rates on longer cables. Not abundant noise and linear design margins often increase the challenge of testing, as manufacturers need to provide ADSL testing instruments with a wider dynamic range and higher accuracy. In short, their testing costs are less than or at least equal to the testing costs of the previous generation of low performance ADSL equipment.

Manufacturers can use single tone testing methods to determine the pure dynamic range, standard distortion, and noise base level of ADSL. This direct testing method is sufficient to quickly detect various defects. The single tone testing method is more effective for testing the signal-to-noise ratio (SNR) of equipment. Although the linearity index of ADSL converters is relatively strict, SNR is still an important device parameter necessary to ensure the correct operation of ADSL. Single tone testing can also measure the overall harmonic distortion (THD) and distortion free dynamic range (SFDR) of the device.

After calculating the SNR, these basic dynamic linear tests only require a small amount of additional processing, so this type of testing will not spend too much testing time overhead. That is to say, the testing time requirement for single tone testing is very moderate relative to its efficiency. In addition, many industry-leading testing systems provide pre made routines to facilitate the development of these single tone tests. Due to the fact that single tone testing methods can test multiple key parameters using a single set of data, most defective devices fail single tone testing.

Although static linear testing is a traditional aspect of the ADC specification, YS1700-000A34 is not suitable for evaluating ADSL devices. The high conversion rate of ADSL ADC is usually offset by high resolution. At this point, it is necessary to capture a large amount of data, which takes up a lot of DSP computation time. Another factor that needs to be considered is the high-frequency signal used in ADSL equipment, and there will be a significant difference between static linear testing and the dynamic response of the device.

Comparing various tests of such devices, it can be found that the most practical effect is still the basic loop back test. The engineer connects the transmitter to the receiver and checks whether the encoded data sent from the output end can be correctly decoded at the input end. Although this highly practical testing method may not provide the necessary information for isolating faulty equipment in complex designs, it is executed very quickly and at the lowest cost.