SA8028 データシートの表示（PDF） - Philips Electronics
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SA8028
Philips Electronics
SA8028 Datasheet PDF : 28 Pages
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Philips Semiconductors
2.5 GHz sigma delta fractional-N /
760 MHz IF integer frequency synthesizers
Product data
SA8028
2.0 SERIAL PROGRAMMING BUS
A simple 3-line bidirectional serial bus is used to program the circuit.
The 3 lines are DATA, CLOCK and STROBE. When the STROBE = 0,
the clock driver is enabled and on the positive edges of the CLOCK
signal, DATA is clocked into temporary shift registers. When the
STROBE = 1, the clock is disabled and the data in the shift register
is latched into different working registers, depending on the address
bits. In order to fully program the circuit, 3 words must be sent in the
following order: C, B, and A. An additional word, the D-word, is for
test purposes only: all bits in this test word should be initialized to 0
for normal operation. The N value of the B-word is stored temporarily
until the A-word is loaded to avoid temporarily false N settings, while
the corresponding fractional ratio Kn is not yet active. When a new
fractional ratio is loaded through the A-word, the fractional sigma
delta modulator is not reset, i.e., it will start the new fractional
sequence from the last state of the previously executed sequence. A
typical programming sequence is illustrated in Figure 10.
When loading several words in series, the minimum STROBE high
time between words must be observed (refer to Figure 8).
Unlike the earlier SA80xx family members, SA8028 has the built-in
feature to output the contents of an addressable internal register.
For the current SA8028, only the momentary division ratio N (RF
divider) can be retrieved through the serial bus. The handshake
protocol requires a “request to read” to be sent prior to each “read”,
i.e., by sending a D-word with the TreadN-bit (<D11>) set to “high”.
Immediately after the transition of “STROBE” from low-to-high,
four (4) clock pulses are needed to prepare the data for output and
another nine (9) clock pulses are needed to accomplish the serial
reading with LSB first. A high-to-low transition of “STROBE” then
resets the serial bus to the input mode. The timing diagram is
presented in Figure 9. In general, a high-to-low transition of the
“STROBE” signal will instantaneously reset the serial bus to the
input mode, even when the chip is in the output mode.
Table 2. Serial bus timing requirements (see Figures 8 and 9)
VDD = VDDCP =+3.0 V; Tamb = +25 °C unless otherwise specified. (Guaranteed by design.)
SYMBOL
PARAMETER
Serial programming clock; CLK
tr
Input rise time
tf
Input fall time
Tcy
Clock period
Enable programming; STROBE
tSTART, tSTART;R Delay to rising clock edge
tW
Minimum inactive pulse width
tSU;E
Enable set-up time to next clock edge
tRESET
Reset data line to input mode
Register serial input data; DATA (I)
tSU;DAT
Input data to clock set-up time
tHD;DAT
Input data to clock hold time
Register serial output data; DATA (O)
tSU;DAT;R
Input clock to data set-up time
MIN.
–
–
100
40
1/fCOMP
20
20
20
20
20
TYP.
10
10
–
–
–
–
–
–
–
–
MAX.
40
40
–
–
–
–
–
–
–
–
UNIT
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
tSU;DAT
tf
tr
TCY
tHD;DAT
tSU;E
CLK
DATA
STROBE
LSB
tSTART
MSB
ADDRESS
>=0
Figure 8. Serial bus “Write” timing diagram.
tW
SR02296
2002 Feb 22
11
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