NJ88C33

6

PHASE COMPARATOR

The phase comparator produces current pulses of

duration equal to the difference in phase between the

comparison frequency (fc=Rl/R), and f

VCO frequency (Fl/N).

When status bit 4 is set high the positive polarity mode of

the output PD is selected. When fc leads f

goes high; when f

Similarly, selecting

the negative polarity mode of PD by programming bit 4 of the

status register low causes PD to have the inverse polarity. The

loop filter integrates the current pulses to produce a voltage

drive to the VCO.

No pulses are produced when locked. The lock detect

output, LD, produces a logic ‘0’ pulse equal to the phase

difference between f

When the phase difference between fc and f

to be resolved by the phase detector then no current pulses

are produced. In this region the loop does not reduce the

close-in noise on the VCO output. This can be overcome

using a very high value resistor to leak a few nanoAmps of

current from the filter and keep the loop on the edge of the

region.

Fig. 5 Phase comparator phase diagram

PROGRAMMING

Transmission Protocol

followed by a sub-address byte followed by 1, 2 or 3 bytes of

data. Bit 7 of the address byte must match the setting of the

S/D pin for the address to be recognised. This allows for

separate addressing of two NJ88C33 synthesisers on the

same bus. The sub-address should be set to select the correct

registers to be programmed and should be followed by the

appropriate number of data bytes.

Registers are not

programmed until the complete message protocol has been

checked.

Each message should commence with a START condition

and end with a STOP condition unless followed immediately

by another transfer, when the STOP condition may be omitted.

Data is transferred from the shift register to the latches on

a STOP condition or by a second START condition.

A START condition is indicated by a falling edge on the

Serial Data line, SDA, when the Serial Clock line. SCL, is high.

A rising edge on SDA when SCL is high indicates a STOP

condition as shown in Fig.6.

Data on SDA is clocked into the NJ88C33 on the rising

edge of SCL. The NJ88C33 acknowledges each byte

transferred to it by pulling the SDA line low for one cycle of SCL

after the last bit has been received.

Serial clock frequency

SCL hold after START

Data set-up time

Data hold after SCL low

SCL set-up before STOP

Symbol

Parameter

f

SCL

t

1

t

2

t

3

t

4

Unit

Min.

Max.

MHz

ns

ns

ns

ns

200

20

0

20

5

I2C TIMING INFORMATION

VDD = 4.5V to 5.5V, Tamb = -40°C to +85°C

Value