Discussion on TD-SCDMA Terminal Production Test

Terminal production testing can use two solutions: signaling mode (comprehensive tester) and non-signaling mode (signal source, signal analyzer). Comprehensive testers are more in line with the signaling consistency of the specification; while signal sources and signal analyzers have greater flexibility, faster speed and better accuracy. TD-SCDMA terminal testing must include support for GSM mode. At the same time, in order to improve the competitiveness of terminal products, TD-SCDMA terminals produced by manufacturers may also include GPS , Bluetooth, WiFi (802.11b/g), DVB and other modes. At present, there is no comprehensive tester on the market that can support these modes at the same time. Therefore, signal sources and signal analyzers have advantages in supporting multiple modes. The weakness of this mode that lacks signaling support can be compensated by the physical layer (L1) signaling simulation software provided by chip manufacturers. As chip manufacturers gradually open up the physical layer (L1) signaling simulation software, the non-signaling mode solution is increasingly valued by terminal manufacturers, which represents a new direction for future terminal testing. Complete terminal production testing includes four aspects: RF transceiver calibration, RF transceiver testing, terminal audio testing, and power supply testing.

This article discusses the production test solution based on signal source, signal analyzer, audio analyzer and communication power supply. For the test of multi-mode terminals, this solution is comprehensive, fast, accurate and flexible. For TD-SCDMA terminal manufacturers, this solution can break the technical monopoly of instrument manufacturers and choose more cost-effective production test instruments. In addition, this solution has the same reference significance for traditional 2G and other 3G terminal manufacturers.

Solution Overview

The instrument composition of this solution includes: RF vector signal source, RF vector signal analyzer, audio analyzer and communication power supply, in addition to RF transceiver coupler and switch array and other equipment, which can perform one-stop overall testing of the terminal in four aspects: RF transceiver calibration, RF transceiver test, terminal audio test and power supply test. This solution can provide one-stop testing of TD-SCDMA, GSM, Bluetooth, WiFi (802.11b/g), DVB , GPS and other modes independently of mode restrictions. Figure 1 is a test case built using Keithley 2910 vector signal source, 2810 vector signal analyzer, 2306 dual-channel power supply and 2015 audio analyzer. The test speed of traditional comprehensive testers is limited by air signaling, which means an increase in test costs for manufacturers. As air signaling of wireless communication, it is actually a problem of mobile phone software. The author believes that it does not need to be strictly verified in the production test stage, but should focus on the hardware characteristics that affect the performance of mobile phones. As a replacement for the signaling part, this solution requires chip manufacturers to provide a physical layer (L1) control command set and control the device under test through a computer interface.

The use of high-speed signal sources and analyzers can break through the bottleneck of instrument speed, making the test speed of the solution almost only depend on the response speed of the device under test, and achieve the maximum test throughput on the production line, thereby improving test efficiency and reducing test costs for manufacturers.

Currently, the accuracy indicators of mid-to-high-end signal sources and analyzers are one level higher than those of comprehensive testers, so high-precision testing can be achieved, test reliability can be increased, and the false detection rate can be reduced, thereby improving test efficiency and reducing test costs.

Discrete test instruments can be flexibly configured according to the specific needs of customers, achieving flexible matching of production line tests, and can effectively solve the "bottleneck effect" and reconfiguration problems between production line test stations.

The following sections will provide specific test recommendations for the four aspects of terminal production testing for reference by TD-SCDMA terminal manufacturers.

TD-SCDMA terminal testing one-stop solution case.

Calibration of RF transceivers

The quality of the terminal's RF performance directly depends on the calibration of the RF transceiver, which is the most important step in production testing.

The calibration of the terminal transceiver includes the calibration of three core parameters: AGC (automatic gain control) voltage, AFC (automatic frequency control) voltage and APC (automatic power control) voltage; the calibration process includes three steps: corresponding test, calibration value calculation (calibration value adjustment) and post-calibration value writing. [page]

1. AGC calibration

The signal received by the RF receiver has a large power range. By adjusting the AGC voltage, the baseband signal amplitude before sampling can be maintained in a constant range. The calibration of the AGC voltage is to measure the correspondence between the control voltage and the received signal power, and write this correspondence to the storage medium, such as E2 ROM. In practical applications, the AGC control voltage may include 1 to 3 levels, respectively represented as AGC1, AGC2, and AGC3. At the same time, the calibration of the AGC may also include the operation of the low noise amplifier (LNA) switch.

The test instrument required for AGC calibration is a radio frequency signal source that can provide a continuous wave (CW) or specific modulation signal with a large power range to the terminal under test.

TD-SCDMA mode AGC calibration operation steps:

1) Use the physical layer signal control command to make the mobile phone enter the TD-SCDMA test mode and open the TD-SCDMA receiver channel;

2) According to the requirements of the AGC algorithm, a group of downlink TD-SCDMA RMC12.2k modulated signals with frequency and power combinations are transmitted in sequence through the signal source list mode;

3) Follow step 2 and read the AGC parameters using the AGC parameter reading instructions provided by the chip manufacturer;

4) Calculate and adjust the AGC parameters, and write the adjusted AGC parameter values ​​back to the E2 ROM using the AGC parameter write instructions provided by the chip manufacturer.

For other modes, such as GSM, the AGC calibration steps are similar to those for TD-SCDMA. The difference is that the terminal chip manufacturer is required to provide physical layer (L1) signaling simulation software and control interface (parallel port, serial port or USB port) for other modes.

2. AFC calibration

AFC calibration is to adjust the reference frequency of the oscillator so that the signal transmitted by the mobile phone has the correct carrier frequency. The calibration method is to set the mobile phone to transmit signals at a series of specific frequencies, use a signal analyzer to test the frequency error of the signal, then calculate the AFC compensation voltage, and write the adjusted AFC voltage into the E2 ROM.

TD-SCDMA mode AFC calibration operation steps:

1) Use the physical layer control command to make the terminal enter the TD-SCDMA test mode and open the TD-SCDMA transmitter channel;

2) Set the frequency and power of the mobile phone's transmitted signal through physical layer signaling simulation instructions;

3) In conjunction with step 2, use the TD-SCDMA demodulation analysis option of the 2810 signal analyzer to measure the frequency error of the terminal's transmitted signal;

4) Calculate and adjust the AFC parameters based on the measured values, and write the adjusted AFC parameter values ​​back to the E2 ROM using the AFC parameter write instruction provided by the chip manufacturer.

For other modes, such as GSM, the AFC calibration steps are similar to those of TD-SCDMA, and the analyzer needs to have the function of analyzing the frequency errors of the signals in these modes.

3. APC calibration

The power value of the RF signal transmitted by the terminal transmitter has a certain control range (power level), and the adjustment of the APC voltage is a method to achieve different transmission powers. The calibration of the APC control voltage is to measure the corresponding relationship between the control voltage and the transmission power, and write this corresponding relationship into the storage medium. The test instrument required for APC calibration is a signal analyzer, which performs instantaneous power test on the RF signal transmitted by the terminal. The measured signal can be a continuous wave signal or a specifically modulated signal. The actual APC circuit may include multiple levels of APC parameters.

TD-SCDMA mode APC calibration operation steps:

1) Use the physical layer control command to make the terminal enter the TD-SCDMA test mode and open the TD-SCDMA transmitter channel;

2) Set the frequency and power of the mobile phone's transmitted signal through physical layer signaling simulation instructions;

3) Follow step 2 and use a signal analyzer to test the signal power;

4) Repeat 2) and 3) until all required frequency and power points are tested;

5) Calculate and adjust the APC parameters based on the measured values, and write the adjusted APC parameter values ​​back to the E2 ROM using the APC parameter write instruction provided by the chip manufacturer.

For other modes, such as GSM, the APC calibration steps are similar to those for TD-SCDMA. The difference is that the terminal chip manufacturer is required to provide L1 signaling simulation software and control interface for other modes.

RF transceiver testing

The test of RF transceiver is the link to check the basic functions and RF performance of the terminal after calibration. Generally speaking, the test of terminal RF transceiver complies with the corresponding communication standard specifications, which clearly stipulate the test principles, test methods and test requirements. The test method recommended by the specification requires the use of an ideal base station simulator, which is very demanding in practical applications. Neither the comprehensive tester nor the signal source and analyzer can be called an ideal base station simulator.

Signal sources and signal analyzers act as base station simulators, which have greater flexibility, faster speed and better accuracy, and are more suitable for large-scale mass production. The signaling weaknesses of signal sources and signal analyzers can be compensated by using the physical layer L1 control commands and control interfaces of chip providers. Therefore, this solution is the direction of future development.

The reference standard for TD-SCDMA terminal transceiver testing is 3GPP TS25.122. For large-scale production testing, it is impossible (not practical) to measure all the required items in the specification. Usually, only key items related to product quality are required to be tested. Further analysis of the protocol shows that the protocol test items include testing of terminal signaling software and terminal transceiver hardware performance. We can not completely follow the test process specified in the protocol, and focus the test items on testing the terminal transceiver hardware performance.

The recommended transmitter test items in production testing are: UE maximum output power, UE frequency stability, closed-loop power control, minimum output power, transmit off power, transmit on/off time template, occupied bandwidth, spectrum emission template, adjacent channel leakage ratio (ACLR), spurious emission, and error vector magnitude.

Here, five indicators are specified: transmitter power, frequency, dynamic power, spectrum and modulation. We can combine these test items. The specific recommended test methods are as follows:

a) Enable the terminal to enter TD-SCDMA 12.2k RMC loopback test mode through physical layer control commands;

b) Set the frequency and set the terminal transmit power to the maximum;

c) Use a signal analyzer to test parameters such as maximum output power, on/off time template, transmit shutdown power, occupied bandwidth, spectrum emission template, spurious emission, adjacent channel leakage ratio (ACLR), frequency error, error vector amplitude, etc. The selected signal analyzer must have the analysis function of these parameters;

d) Change the frequency and repeat c) until the test of the three frequencies (high, medium and low) required by the standard is completed;

e) Set the frequency point and the transmit power according to the power/time relationship (A~G segment) required by the closed-loop power control, and use a signal analyzer to complete the dynamic power test;

f) Set the power to minimum and complete the minimum transmit power test

g) Change the frequency and repeat e) until the required frequency test is completed.

The recommended receiver test items in production testing are: reference receiving sensitivity and maximum input level, which is actually the receiving bit error rate test.

According to the test method required by the 3GPP 34.122 standard, we can perform the test in the following steps:

a) Enable the terminal to enter TD-SCDMA 12.2k RMC loopback test mode through physical layer control commands;

b) Generate the signal required for BER test through the signal source. The selected signal source shall have the function of generating TD-SCDMA waveform of sufficient length. Set the signal power according to the power level required by the reference receiving sensitivity and the maximum input level.

c) The terminal demodulates the received signal and transmits the demodulated bits back to the computer through the control interface (parallel port, serial port or USB port), and calculates the BER using the PN9 BER calculation formula provided by the chip manufacturer. Compare the BER with the standard requirements. [page]

For other modes such as GSM, we can use similar methods to develop test items according to standards.

Terminal audio test

Voice communication is the main function of the terminal and an important aspect of user evaluation of terminal performance. Therefore, strict audio testing of the terminal is an important aspect of terminal production testing.

Today's mobile terminals integrate more multimedia functions, and in order to distinguish themselves from traditional mobile phones, their audio capabilities must also be improved or enhanced. Although voice calls can still use mono and relatively low fidelity, music and video functions require higher sampling rates to achieve high-quality stereo reproduction.

Therefore, it is recommended to divide the terminal audio test into two aspects: voice communication audio test and multimedia function audio test. The instrument used is Keithley 2015 audio analyzer.

1. Voice communication audio test

For TD-SCDMA terminals (including GSM mode and TD-SCDMA mode), the standards we need to refer to are 3GPP TS 51.010, TS26.131 and TS26.132. The following are the audio test items specified in the standards.

In actual production, the above test items are generally simplified to the measurement of voice response level, frequency response characteristics, distortion and noise during voice communication.

Test Method:

a) Install the mobile phone on the test stand and seal the artificial ear and the headphone jack of the mobile phone;

b) Make the terminal enter the voice loopback mode through physical layer signaling simulation instructions;

c) An audio analyzer is connected to an artificial mouth, sending a pure single tone with a rated sound pressure value at the reference point, varying the frequency according to the standard;

d) The audio analyzer is connected to the artificial ear to test the output level, frequency response characteristics, distortion and noise of the artificial ear.

2. Multimedia function audio test

For new audio products (such as MP3 and MD, etc.), there are special testing requirements for CODEC encoders/decoders. It is necessary to input multi-tone test signals at the same time (for example, 31 multi-tone signals need to be generated from the frequency range of 22Hz-20kHz according to the distribution of 1/3OCTAVE and output at the same time) to test the response of the CODEC.

Such testing can be done with the help of a professional audio analyzer and professional audio analysis software.

Power supply test

The battery calibration, power consumption characteristics and charging characteristics of the terminal are tested through the power supply. The dual-channel power supply equipment can perform professional power supply testing on the terminal. This test method is widely used in traditional production lines and will not be discussed in detail here.