SBAS717A June 2015 – June 2015 ADS58J63
Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.
The following steps are recommended as the power up sequence with the ADS58J63 in 2x complex decimation mode (DDC Mode 0) with LMFS = 4841 (shown in Table 63).
|STEP||DESCRIPTION||REGISTER ADDRESS||REGISTER DATA||COMMENT|
|1||Supply all supply voltages. There is no required power supply sequence for the 1.15-V supply, 1.9-V supply and 3-V supply, and these may be supplied in any order.||—||—||—|
|2||Pulse a hardware reset (low to high to low) on pin 48.||—||—||—|
|Alternatively it can be reset with:
Analog reset and Digital reset
|3||Set input clock divider||11h
|Select master page
Set clock divider to /2
|4||Reset interleaving correction engine. Register access default into page 68h||6000h
|Channel AB (and channel CD since device is in broadcast mode)|
|5||Default registers for JESD analog page||4003h
|Select JESD analog page
PLL mode 40x for Channel AB and CD
|6||Default registers for JESD digital page||4003h
|Select JESD digital page
Set CTRL K for channel AB and CD
Set K to 16
|7||Enable single SYNCb input (SYNCAB)||4005h
|Disable broadcast mode
Use SYNCAB for channel C/D
|8||Pulse SYNCb (pin 55/56) from low to high to transmit data from k28.5 sync mode||—||—||—|
|t1||Power-on delay||Delay from power up to active high RESET pulse||1||ms|
|t2||Reset pulse duration||Active high RESET pulse duration||10||ns|
|t3||Register write delay||Delay from RESET disable to SEN active||100||ns|
The signal to noise ratio of the ADC is limited by three different factors: the quantization noise is typically not noticeable in pipeline converters and is 84 dB for a 14-bit ADC. The thermal noise limits the SNR at low input frequencies while the clock jitter sets the SNR for higher input frequencies.
The SNR limitation resulting from sample clock jitter can be calculated following:
The total clock jitter (TJitter) has two components – the internal aperture jitter (120 fs for ADS58J63) which is set by the noise of the clock input buffer and the external clock jitter. It can be calculated as following:
External clock jitter can be minimized by using high-quality clock sources and jitter cleaners as well as band-pass filters at the clock input while a faster clock slew rate also improves the ADC aperture jitter.
The ADS58J63 has a thermal noise of approximately 72 dBFS and an internal aperture jitter of 120 fs.
The ADS58J63 provides several different options to output test patterns instead of the actual output data of the ADC in order to simplify bring up of the JESD204B digital interface link. The output data path is shown in Figure 139
The ADC test pattern replaces the actual output data of the ADC. The following test patterns are available in register 74h. In order to get the test pattern output propoerly, the interleaving correction needs to be disabled (6100h, address 18h) and burst mode enabled (DDC disabled).
Burst mode only supports LMFS = 4421 (DDC Modes have different configurations) and test pattern switches between 9-bit (low resolution) and 14-bit (high resolution) output. See Table 65
|D7-D4||TEST PATTERN||0000||Test pattern output on channel A and B
0000 Normal Operation using ADC output data
0001 Outputs all 0s
0010 Outputs all 1s
0011 Outputs toggle pattern: Output data are an alternating sequence of 101010101010 and 010101010101
0100 Output digital ramp: output data increments by one LSB every clock cycle from code 0 to 16384
0110 Single pattern: output data is custom pattern 1 (75h and 76h)
0111 Double pattern: output data alternates between custom patter 1 and custom pattern 2
1000 Deskew pattern: output data is 2AAAh
1001 SYNC pattern: output data is 3FFFh
The Transport Layer maps the ADC output data into 8bit octets and constructs the JESD204B frames using the LMFS parameters. Tail bits or ‘0’s are added when needed. Alternatively the JESD204B long transport layer test pattern can be substituted as shown in Table 66 .
|D4||TESTMODE EN||0||Generates long transport layer test pattern mode according to clause 188.8.131.52 of JESD204B specification
0 = test mode disabled
1 = test mode enabled
The Link Layer contains the scrambler and the 8b/10b encoding of any data passed on from the Transport Layer. Additionally it also handles the initial lane alignment sequence which can be manually restarted. The Link Layer test patterns are intended for testing the quality of the link (jitter testing etec). The test patterns do not pass through the 8b/10b encoder and contain the options shown in Table 67.
|D7-D5||LINK LAYER TESTMODE||000||Generates pattern according to clause 184.108.40.206.2 of the JESD204B document
000 normal ADC data
001 D21.5 (high frequency jitter pattern)
010 K28.5 (mixed frequency jitter pattern)
011 Repeat initial lane alignment (generates K28.5 character and repeat lane alignment sequences continuously)
100 12 octet RPAT jitter pattern
Furthermore a 215 PRBS can be enabled by setting up a custom test pattern (AAAA) in the ADC section and running that through the 8b/10b encoder with scrambling enabled.
The ADS58J63 is designed for wideband receiver applications demanding excellent dynamic range over a large input frequency range. A typical schematic for an AC coupled dual receiver (dual FPGA with dual SYNC) is shown below.
By using the simple drive circuit of Figure 140 (when AMP drives ADC) or Figure 51 (when transformers drive ADC), uniform performance can be obtained over a wide frequency range. The buffers present at the analog inputs of the device help isolate the external drive source from the switching currents of the sampling circuit.
For optimum performance, the analog inputs must be driven differentially. This architecture improves the common-mode noise immunity and even-order harmonic rejection. A small resistor (5 Ω to 10 Ω) in series with each input pin is recommended to damp out ringing caused by package parasitics, as shown in Figure 140.