We would like to use OSCOUT output as a reference for next HMC7044 OSCIN input (in cascade). The problem is that we measured phase noise of the OSCOUT output with greater jitter than we expected - compared to CLKOUT outputs.
For DCLK we measured circa 200fs and for OSCOUT output we got 260fs (integration bandwidth 10Hz - 20MHz).
We are using CVSS-945. It should have circa 100fs according to the datasheet (calculated from https://abracon.com/phaseNoiseCalculator.php).
We haven´t found any information about OSCOUT parameterers in HMC7044´s datasheet so we miss practical usage of this output.
Can you please help us?
I have the same question about the quality of OSCOUT outputs.We too want to link the HMC7044s and are concerned about the added phase noise.I have an additional comment on an undocumented feature on these outputs in CMOS mode.This concerns registers 0x3A and 0x3B :In CMOS mode (bit[5:4] = 0b11) the bits[2:1] that are used for the impedance of the CML mode are now used to activate pins P and N0x31 (bit[2:1] = 0b00) : no active pin0x33 (bit[2:1] = 0b01) : output on OSCOUTx_P0x35 (bit[2:1] = 0b10) : output on OSCOUTx_N0x37 (bit[2:1] = 0b11) : output on OSCOUTx_P and OSCOUTx_N (with the same polarity)I found this by accident and even the "HMC7044 Configuration GUI v0.5.3" software on the evaluation board does not take it into account.Are you aware of any other undocumented functions?Is a revision of the datasheet planned ?
I reply to myself : with "HMC7044 GUI 1.0.0" the menu takes into account the management of outputs in CMOS mode
I will check if there are any other undocumented features ...
Hi Dan The OSCOUTs are the buffered version of input signal at OSCIN. However the noise floor of OSCOUT buffers is not as good as CLKOUT buffers. On the other hand, CLKOUT outputs are synthesized outputs with very high performance buffers. The disadvantage is the in-band noise will be higher because it is re-synthesized.Considering only integrated noise may be misleading in some applications such as this one. The OSCOUT may have higher jitter (than OSCOUT) but it should give better results when used as the reference source for a PLL because the far out noise will be filtered out depending on the LBW.I recommend making some simulations with ADIsimPLL tool by modeling the phase noise profile of outputs.
You are right, in CMOS mode, impedance bits are used to enable the outputs.
The OSCOUT buffers are using the bias values defined in 0x009F (low power setting) and there is not any selection for low/high power such as CLKOUTs. If higher power is needed for OSCOUTs, the values for 0x009F and 0x00A0 can be exchanged (0xDF to 0x009F and 0x4D to 0x00A0). Note that, the High Performance bit should be inverted accordingly for all CLKOUTs and SCLKOUTs as well.