Hello all,

I am RF engineer working on frequency synthesizers.

My request is about the HMC698LP5.

In the application circuit shown in its datasheet (at the end of the document) http://

www.analog.com/media/en/technical-documentation/data-sheets/hmc698.pdf

- How the Voltage (7 V for HMC529) for 13 GHz locked frequency is set?

No external voltage is applied. It is the HMC698LP5 auto lock function?

Using the example 13 GHz:

The reference frequency (100 MHz) is fixed. Then we set the N and S bits for 13

GHz, we apply Vcc and the HMC698LP5 locks itself? Is this the procedure?

If this is the case, could you explain how N and S have been calculated?

(S1, N4 and N5 bits in on state).

Many thanks for your help,

Regards

1wallow CountreHi there,

The NU / ND outputs a 2V pulse (because of the internal 200 ohm resistor on collector - see equivalent schematic in DS). The PFD filter that falls between the HMC698 & the active loop filter has a matching 200 ohm resistor - this must remain at 200 ohms. The op amp with it's resistive feed back amplifies this to a maximum of about 13.8V (assuming we have applied the full15V to Vcc on the op amp). The phase detector compares the reference signal to the divided down VCO signal and automatically adjusts this voltage until the first the frequency is close enough then finally until the phases match. It continues to output voltage pulses at the PFD rate rapidly moving the tuning voltage up and down to keep these 2 signals "locked" in phase.

N will need to be 6500MHz / 100MHz = 65; this allows us to divide our 6500MHz signal down to 100MHz for comparison with our reference. The reason we are dividing 6500MHz instead of 13000MHz is because although our output frequency will be 13000MHz, the frequency that we are feeding back to the PLL for comparison is the 6500MHz coming from the RFout/2 port of our VCO.

This part uses a dual modulus prescaler so the minimum continuous range for N is set by P*(P-1) = 4*(4-1) = 4*3 = 12. As long as our N value is greater than or equal to "12" we don't need to worry about this. In our case N = 65 so this value is fine.

Now if we divide N by our prescaler value of 4 we get 16d which will be the value of our N counter with a remainder (or modulus) of 1d.

The value for the N Counter will be 16d - 1d = 15d and the swallow counter (S) will be 1d. Convert these to binary values and you're done!

The datasheet lists the LSB first so be sure to make note of this when comparing your values.

65d / 4d = 16d Remainder = 1

Best Regards,

Marty