UMA1015M Datasheet, PDF(5/24 Page) NXP Semiconductors – Low-power dual frequency synthesizer for radio communications

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UMA1015M Datasheet, PDF (5/24 Pages) NXP Semiconductors – Low-power dual frequency synthesizer for radio communications

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Philips Semiconductors

Low-power dual frequency synthesizer

for radio communications

Product speciï¬cation

UMA1015M

Table 1 Synthesizer ratio of reference divider

SYNTHESIZER A SYNTHESIZER B

Phase comparators

For each synthesizer, the outputs of the main and

reference dividers drive a phase comparator where a

charge pump produces phase error current pulses for

integration in an external loop filter. The charge pump

current is set by an external resistance RSET at pin ISET,

where a temperature-independent voltage of 1.2 V is

generated. RSET should be between 12 kâ¦ and 60 kâ¦ (to

give an ISET of 100 ÂµA and 20 ÂµA respectively).

The charge-pump current, ICP, can be programmed to be

either (12 Ã ISET) or (24 Ã ISET) with the maximum being

2.4 mA. The dead zone, caused by finite switching of

current pulses, is cancelled by an internal delay in the

phase detector thus giving improved linearity. The charge

pump has a separate supply, VCC, which helps to reduce

the interference on the charge pump output from other

parts of the circuit. Also, VCC can be higher than VDD1 if a

wider range on the VCO input is required. VCC must not be

less than VDD1.

Voltage doubler

If required, there is a voltage doubler on-chip to supply the

charge pumps at a higher level than the nominal available

supply. The doubler operates from the digital supply VDD1,

and is internally limited to a maximum output of 6 V.

An external capacitor is required on pin VCC for smoothing,

the capacitor required to develop the extra voltage is

integrated on-chip. To minimize the noise being introduced

to the charge pump output from the voltage doubler, the

doubler clock is suppressed (provided both loops are

in-lock) for the short time that the charge pumps are active.

The doubler clock (RF/64) is derived from whichever main

divider is operating (synthesizer A has priority). While both

synthesizers are powered down (and the doubler is

enabled), the doubler clock is supplied by a low-current

internal oscillator. The doubler can be disabled by

programming the bit VDON to logic 0, in order to allow an

external charge pump supply to be used.

output is forced LOW). The lock condition output is

software selectable (see Table 4). An out-of-lock condition

is flagged when the phase error is greater than T00L, the

value of which is approximately equal to 80 cycles of the

relevant RF input. The out-of-lock flag is only released

after 8 consecutive reference cycles where the phase error

is less than T00L. The out-of-lock function can be disabled,

via the serial bus, and the pin P0/OOL can be used as an

output port. Three other port outputs P1, P2 and P3

(open-drain transistors) are also available.

Serial programming bus

A simple 3-line unidirectional serial bus is used to program

the circuit. The 3 lines are DATA, CLK and E (enable). The

data sent to the device is loaded in bursts framed by E.

Programming clock edges are ignored until E goes active

LOW. The programmed information is loaded into the

addressed latch when E returns inactive HIGH. This is

allowed when CLK is in either state without causing any

consequences to the register data. Only the last 21 bits

serially clocked into the device are retained within the

programming register. Additional leading bits are ignored,

and no check is made on the number of clock pulses. The

fully static CMOS design uses virtually no current when the

bus is inactive. It can always capture new programming

data even during power-down of both synthesizers.

However when either synthesizer A or synthesizer B or

both are powered-on, the presence of a TCXO signal is

required at pin 8 (fXTALIN) for correct programming.

Data format

Data is entered with the most significant bit first. The

leading bits make up the data field, while the trailing four

bits are an address field. The address bits are decoded on

the rising edge of E. This produces an internal load pulse

to store the data in the addressed latch. To ensure that

data is correctly loaded on first power-up, E should be held

LOW and only taken HIGH after having programmed an

appropriate register. To avoid erroneous divider ratios, the

pulse is inhibited during the period when data is read by

the frequency dividers. This condition is guaranteed by

respecting a minimum E pulse width after data transfer.

The data format and register bit allocations are shown in

Table 2.

Out-of-lock indication/output ports

There is a lock detector on-chip for each synthesizer. The

lock condition of each, or both loops, is output via an

open-drain transistor which drives the pin P0/OOL (when

out-of-lock, the transistor is turned on and therefore the

1995 Jun 22

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