Philips Semiconductors

Product data

SA8028

2.5 GHz sigma delta fractional-N /

760 MHz IF integer frequency synthesizers

2002 Feb 22

9

1.4

Phase detector (see Figure 6)

The reference signal and the RF (IF) divider output are connected to a phase frequency detector that controls the charge pumps. The dead

zone (caused by the finite time taken to switch the charge pump current sources on or off) is cancelled by forcing the pumps ON for a minimum

time (backlash time,

τ) at every cycle providing improved linearity.

SR02413

R

X

P

N

* see note

IF/RF

DIVIDER

D

Q

CLK

“1”

R

D

R

CLK

“1”

X

Q

N

P

τ

P–TYPE

CHARGE PUMP

N–TYPE

CHARGE PUMP

R

τ

τ

NOTES:

For the RF synthesizer, the output of the reference input buffer is routed directly (not divided) to the input of the RF phase detector. Whereas

for the IF synthesizer, the reference input to the IF phase detector is the output from the reference divider.

τ (backlash time) is the delay that fixes the minimum allowable charge pump activity time.

Figure 6.

Phase detector structure with timing.