Datasheet NJ88C50IG, NJ88C50NPAS, NJ88C50 Datasheet (MITEL)

Page 1

The NJ88C50 is a low power integrated circuit, designed as the heart of a fast locking PLL subsystem in a mobile radio application. It is manufactured on Mitel Semiconductor 1.4 micron double polysilicon CMOS process, which ensures that low power and low noise performance is achieved. The device contains two synthesisers, one for the generation of VHF signals up to 125MHz and a second for UHF (when used with a mulitmodulus prescaler such as the SP8713/14/15). The main synthesiser has the capability of driving a dual speed loop filter and also can perform Fractional-N interpolation. Both synthesisers use current source outputs from their phase detectors to minimise external components. Various sections may be powered down for battery economy.

FEATURES

■ 30MHz main synthesiser

■ 125MHz auxiliary synthesiser

■ Programmable output current

from phase detector - up to 10mA

■ High input sensitivity

■ Fractional-N interpolator

■ Supports up to 4 modulus prescalers

■ SSOP package

APPLICATIONS

■ NMT, AMPS, ETACS cellular

■ GSM, IS-54, RCR-27 cellular

■ DCS1800 microcellular

■ DLMR, DSRR, TETRA

■ DECT, PHP cordless telephones

NJ88C50

Dual Low Power Frequency Synthesiser

DS3805 - 1.8 July 1995

NP20

Fig.1 Pin assignment

ABSOLUTE MAXIMUM RATINGS

Storage temperature -55°C to +150°C Operating temperature -40°C to +85°C Supply voltage -0.5 to 7.0V Voltage on any pin -0.3V to (VDD + 0.3V)

ORDERING INFORMATION

NJ88C50\IG\NPAS - (Industrial temp range in SSOP

package)

Fig.2 Simplified block diagram

Page 2

NJ88C50

ARCHITECTURE

Fig.2 shows a simplified block diagram of the NJ88C50, a more detailed description of each block and its function is given later in this datasheet.

The synthesiser consists of the following blocks

- 35MHz reference frequency input buffer

- 35MHz programmable reference divider

- 125MHz Auxiliary synthesiser input buffer

PIN DESCRIPTION

1 2

3 4

5 6 7 8 9 10 11 12 13 14 15 16

17 18 19 20

Name

AVDD FIM

FIMB DATA

CKIN STROBE RI FIA RSA PDA PDI GND PDP VDD RSM RSC

SCREEN MOD1 MOD2 AGND

Function

Analog supply pin (nominally 5V). Main synthesiser balanced input buffer, may be used with single ended prescaler output if Fimb is biased. Main synthesiser balanced input buffer, may be used with balanced prescaler output, or biased for single ended operation. Serial input for programming data. Serial clock input for programming bus. Program enable pin, active low. Master reference frequency input, should be a.c coupled from an accurate source. Auxiliary synthesiser frequency input, should be a.c coupled. Current setting resistor connection defining auxiliary phase detector output current. Tristate current output from auxiliary phase detector. Tristate current output from the main synthesiser's phase detector giving integral control. Digital ground supply pin. Tristate current output from the main synthesiser's phase detector giving proportional control. Digital supply pin (nominally 5V). Current setting resistor connection defining main synthesiser's phase detector output currents. Current setting resistor connection defining the compensation current for fractional-N ripple elimination in the main synthesiser's current source outputs. To be connected to ground to provide isolation of the modulus control pins from RF interference. Modulus control pin (see truth table). Modulus control pin (see truth table). Analog ground supply pin.

- 125MHz Auxiliary synthesiser programmable divider

- Auxiliary synthesiser phase detector with current source outputs

- 30MHz main synthesiser input buffer (differential inputs)

- 30MHz main synthesiser programmable divider and control logic

- Main synthesiser Fractional-N interpolation system

- Main synthesiser phase detector with dual current source outputs

It is recommended that power supply pins are well decoupled to minimise power rail born interference.

Page 3

NJ88C50

FUNCTIONAL DESCRIPTION

The NJ88C50 has been designed using a modular concept, and its operation can be best summarised as these component blocks.

Reference divider

The reference divider is used to provide the reference signals needed for both the main and auxiliary synthesiser phase detectors. The divider allows for a twelve bit number to be loaded, via the serial bus, to select the required division ratio. Division ratios of 3 to 4095 can be used.

The reference divider input stage will accept a low level, AC coupled, sinewave input. It is anticipated that in most systems this will be provided by a stable reference source up to 35MHz, and so encompasses all the common TCXO (temperature controlled crystal oscillator) frequencies, such as 9.6, 12.8, 13.0, 19.44 and 26MHz.

A standby mode is supported so that the reference divider can be powered down, this is achieved using two of the serial program control bits.

To reduce the possibility of unwanted interaction between the main and auxiliary synthesisers, the charge pumps do not take current at the same time. To achieve this the output of the reference divider has a duty factor of approximately 50:50, which then allows the Q and QBAR taps to be used for the auxiliary and main synthesisers respectively. By doing this the current pulses can be taken alternatively, minimising modulation of the power supply rails as current is drawn. The reference divider consists of a 12 bit programmable divider followed by a 4 bit binary counter. This 4 bit counter gives a choice of divide by M, 2M, 4M or 8M.

A pair of programmable control bits are used to determine which of the divide by M, 2M, 4M or 8M outputs is supplied to the auxiliary synthesiser’s phase detector and a further pair of control bits are used to determine which are supplied to the main synthesiser’s phase detector.

The charge pump output current level is set by an external resistor on the RSA pin (pin 9) up to a limit of 250µA +/-10%. A pull up current pulse will indicate that the VCO frequency must be increased, whilst a pull down pulse indicates that the frequency must be decreased.

Fig.3 Auxiliary phase detector

Main Synthesiser

The main synthesiser is capable of operating at frequencies up to 30MHz. The synthesiser uses the 12 bit reference divider, shared with the auxiliary synthesiser, a 12 bit up/down N divider and a digital phase comparator with current source outputs.

The device also has a number of features which increase the design flexibility and performance of the synthesiser. These include fractional-N operation, speed up mode and support of 2, 3 and 4 modulus prescalers. A description of the

operation and advantages of each of these features is given.

Auxiliary synthesiser

The auxiliary synthesiser operates over an input frequency range from 1 to 125MHz, without the use of an external prescaler. The synthesiser consists of a 12 bit N divider and a digital phase comparator with current source outputs. The reference frequency is supplied by the shared reference divider. Current source outputs allow a passive loop filter to be used.

When the auxiliary synthesiser is not in use, a standby mode is supported so that power consumption is reduced. This is achieved using one of the serial program control bits.

The divider is programmed with a 12 bit word allowing division ratios of 3 to 4095 to be used.

The auxiliary phase detector consists of the 2 D-type phase and frequency detector shown in Figure.3 below, the high and low outputs of which drive on-chip, opposing complementary charge pumps. This type of phase detector design eliminates non linearity or deadband around the zero phase error (locked) condition.

The main N divider input buffer will accept inputs from an external prescaler, either as balanced (2 wire) ECL levels at frequencies up to 30MHz, or DC coupled to a single ended prescaler output. Single ended operation requires the other buffer input (pin 3) to be externally biased to the correct slicing voltage for the prescaler and also externally decoupled.

If the inputs are in the form of balanced ECL levels, there must not be a skew of greater than 2ns between one input changing and the second input changing. The relationship of the signals is shown below in Fig.4.

Fig.4 Maximum input skew

Page 4

NJ88C50

The main N divider is programmable so that it can determine how many cycles of each division ratio the external prescaler will perform.

The total division ratio of the output from the system VCO to the synthesiser's phase detector may be expressed as NTOT and R1, R2, R3 and R4 are the available prescaler ratios and N1, N2, N3 and N4 are the corresponding number of cycles for each ratio selected, within one complete division cycle.

The divider is programmed via the serial data bus and the values needed to be programmed for each of the possible prescaler ratios are as follows:-

In 2 modulus mode (division ratios R1, R2)

NTOT = N1.R1 + N2.R2

Programmed values needed: N1 - a 12 bit value giving the number of times R1 is to be used N2 - a 8 bit value giving the number of times R2 is to be used

In 3 modulus mode (division ratios R1, R2, R3)

NTOT = N1.R1 + N2.R2 + N3.R3

Programmed values needed: N1 - a 12 bit value giving the number of times R1 is to be used N2 - a 4 bit value giving the number of times R2 is to be used N2+N3 - a 4 bit value where N3 is the number of times R3 is to be used and (N2+N3) is modulo-16 addition

If N2, N3, or N4 are set to zero this will give a full count of 16 for the corresponding modulus.

The N divider block also has a special control line from the Fractional-N logic. When required this control will cause the total division ratio to be increased from N to N+1. This is achieved by forcing a cycle which would have normally used a prescaler ratio R1 to use ratio R2 instead. R1 and R2 are chosen so that R2 equals R1+1.

Further explanation of the operation of the synthesiser when using 2, 3 or 4 modulus prescaler is given in the section on multimodulus division (page 8).

The phase detector used on the main synthesiser is similar to the type used on the auxiliary synthesiser (Figure.3). In this case, however, the detector will drive two pairs of complimentary charge pumps, one of which is intended to drive the loop integrator capacitor to provide integral control, whilst the other provides proportional control for the VCO. This system is shown in Fig 5, and has applications where fast locking of the loop is required.

In 4 modulus mode (division ratios R1, R2, R3, R4)

NTOT = N1.R1 + N2.R2 + N3.R3 + N4.R4

To facilitate the use of multimodulus prescalers the N divider is based upon a twelve bit up/down counter which functions as follows

The first value, N1, is loaded into the counter which then counts down from N1 to zero. During this time, the modulus ratio R1 is selected.

When the counter reaches zero modulus R2 is selected and the counter then counts up to the N2 value. If 2 modulus operation is chosen, the counter is then reloaded with N1 and the count is repeated.

For operation with 3 or 4 modulus devices, the counter continues to count up once it has reached the N2 value. The count continues to the N2+N3 value and during this time the R3 ratio is selected. In the 3 modulus case, when the N2+N3 value is reached the counter is then reloaded with the N1 value and the modulus ratio R1 is selected.

For 4 modulus operation the counter will continue its count up to the N2+N3+N4 value before reloading the N1 value. During this time the R4 modulus is selected.

Fig.5 Loop filter using both charge pumps

MODES OF OPERATION

Normal Mode

The synthesiser will operate in normal mode while the strobe line of the serial data bus is low. In this mode the following current levels are produced. The charge pump providing the proportional feedback term will have a normal current level designated by Iprop(0), that is set by an external bias resistor, RSM. Iprop(0) will vary when different N-divider ratios are programmed, so that it is proportional to the total division ratio. To avoid the necessity of computing the total division ratio on chip, an eight bit number representing the most significant bits of Ntot will be loaded via the serial data bus. Iprop(0) is therefore given by

Iprop(0) = CN.Ibo

where CN is the loaded eight bit number and the value Ibo is scaled from the external current setting resistor RSM where Ibo = Irsm/32. Typically Ibo = 1µA ,and therefore Iprop(0) will have a maximum value equal to 255µA.

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NJ88C50

The normal value of Iprop, Iprop(0), is obtained while the strobe line of the serial programming bus is held low. In this condition, the second charge pump providing the integral feedback term is inactive.

Speed up Mode

In speed up mode the loop bandwith during switching is increased to allow faster initial frequency acquisition. This is done by using the dual phase detector outputs (PDP and PDI) connected to a standard passive loop filter as shown in fig.5. The effect of this is to increase the loop gain and hence the bandwidth while maintaining a constant phase margin

when switching between speed up mode and normal mode.

The synthesiser operates in speed up mode when the strobe line goes high loading either word A or word A2 (see programming section Page 8-Page 9) and it will stay in this mode until the strobe line goes low. In this mode the following current levels are produced. The charge pump providing the proportional feedback will increase its current from Iprop(0) to a value Iprop(1), where

Iprop(1) = 2

L+1

.Iprop(0)

where L is a two bit number loaded as part of the serial programming data. Iprop(1) will therefore be 2, 4, 8 or 16 times Iprop(0). The charge pump supplying Iprop is specified up to a value of 1mA.

Also when the strobe line goes high loading word A or word A2, the charge pump providing the integral feedback term becomes active at a current level Iint given by

Iint = K.Iprop(1)

ratio. Using fractional-N the value of N is alternated between N and N+1 in order to simulate a fractional part. For example

9000.375 would be simulated by alternating between 9000 and 9001 in the pattern

9000, 9000, 9001, 9000, 9000, 9001, 9000, 9001 (mean value of 9000.375).

On the NJ88C50 the fractional-N circuit consists of an accumulator which can be set to overflow at a value of 5 or 8 (FMOD in programming word D, see page 9). The value in the accumulator, A, is incremented once every comparison cycle of the main phase detector and every time the accumulator overflows the total division ratio of the synthesiser and prescaler is increased from N to N+1. To obtain the pattern described above N=9000 and FMOD would be set to mod8 and the incremental value, NF(programmed in word A) would be set to 3. The accumulator would then behave as shown below.

Increment Accumulator Total Division

Value Value Ratio

3 3 9000 3 6 9000 3 1 9001 3 4 9000 3 7 9000 3 2 9001 3 5 9000 3 0 9001

Varying NF allows different fractions to be obtained. If NF=1 and FMOD=8 the accumulator would overflow once in every 8 cycles giving a value of 9000.125. Similarly if NF=4 the accumulator overflows every other cycle giving 9000.5.

where K is a four bit number loaded as part of the serial programming data. Although Iint can be programmed to be 240 times greater than Iprop(0), the charge pump supplying Iint is only specified up to a value of 10mA.

For all charge pumps, a pull-up current indicates the VCO frequency should be increased while a pull-down current indicates the VCO frequency should be decreased.

For the proportional and integral charge pumps, the selected pulse current levels will remain substantially constant over the charge pumps output voltage ranges tabulated in the electric characteristics. “Substantially constant” means that the current will not have changed by more than 10% of the value measured at 2.5 volts on the output .

FRACTIONAL-N OPERATION

Conventional, non fractional-N synthesisers have a frequency resolution or step size equal to the phase detector comparison frequency. Fractional-N refers to a technique which allows finer frequency steps to be obtained.

The synthesised frequency with a conventional synthesiser is equal to N times the phase detector comparison frequency, where N is the programmable integer loop divide

For a given step size this increase in resolution means a higher comparison frequency at the phase detector, and therefore a lower overall division ratio. For example,

with a step size = 200kHz and carrier frequency = 900MHz

Non fractional-N synthesiser Comparison frequency=200kHz Division ratio=900MHz=4500

200kHz Fractional-N synthesiser (using 5ths)

Comparison frequency=1MHz Division ratio=900MHz=900

1MHz In most applications the phase noise is proportional to the

overall division ratio. Therefore fractional-N gives lower phase noise. This higher comparison frequency and lower phase noise allows circuits to be built with wider loop bandwidths while keeping the same stability. This means that phase locked loops (PLLs) can be made to either switch faster for a given phase noise or be quieter for a given switching speed, compared to conventional designs.

Page 6

NJ88C50

However the alternation between the N and N+1 values causes a ripple in the output frequency. This ripple is not desirable in radio frequency synthesisers. This ripple or jitter waveform is predictable from the pattern of N and N+1 values and so can be cancelled.

The instantaneous accumulator value, A, is proportional to

the cumulative frequency error caused by ignoring the fractional part during the periods of the divide by N. The accumulator value, A, may therefore be used to generate a waveform corresponding to the jitter waveform, that is then used to cancel the jitter out of the phase detector. This jitter compensation current pulse is equal to A.Icomp where Icomp

represents the step size as A is incremented.

Corresponding to the two alternative values of Iprop,

Iprop(0) and Iprop(1), Icomp will take the values Icomp(0) and Icomp(1). Icomp is always pull-up, and the magnitude of its steps for perfect jitter compensation are related to the value of Iprop by the factors

0 , 1/Q.Ntot , 2/Q.Ntot , 3/Q.Ntot ........ Q-1/Q.Ntot

where Q = accumulator modulus in use (5 or 8)

Since

Iprop(0) = CN.Ibo

and CN is an approximation to Ntot apart from a scaling factor, the value of Icomp(0) required becomes independent of Ntot and its steps are

0 , 1/Q , 2/Q , 3/Q ........ Q-1/Q times Ibo.(scaling factor)

where scaling factor = Max. value of CN to be used

Corresponding max. value of Ntot

therefore Ico = 1 x CN(max) x Ibo

Q Ntot(max)

and Icomp(0) = A.Ico

where Ico is scaled from the external current setting resistor RSC.

Ico = Irsc/128.

Typically Ntot(max) might be 10000, with CN(max)=250 and Q=8, so the current step will be of magnitude Ibo/320. Since Ibo is only 1 uA, this is a very small value; however this value only applies if Icomp is a continuous current. Icomp however will be a short current pulse coincident with the Iprop pulse, in order to cancel jitter components over the widest possible frequency range.

When the duty factor of Icomp is taken into account, its pulse value may be increased accordingly. Icomp is therefore generated as a pulse of fixed width equal to two periods of the input reference clock frequency, with a timing that straddles the active edge of the reference divider output pulse supplied to the main phase detector, as shown below: (Fig 6).

Since the duty factor of Icomp is 2/M and depends on the value of M programmed, it is possible to set the peak pulse value of Icomp(0) by means of the external current setting resistor RSC to correspond with the value of M intended, the value of ‘scaling factor’ defined above, the accumulator modulus Q and the value of Ibo set by the other current setting resistor.

therefore Ico = 1 x Nmax x M x Ibo

Q Ntot(max) 2

This gives a typical value for Ico of 0.1µA. The two values of Icomp, Icomp(0) and Icomp(1) are related

Icomp(1) = 2

L+1

.Icomp(0)

Icomp(0) occuring when the strobe line is low and Icomp(1) occuring when the strobe line is high loading either WORDA or WORDA2 (see programming section, page 8 and 9) .

Corresponding to the pull-up pulse Icomp(1) that is added to the proportional charge pump pulse Iprop(1), there is also a pull-up current pulse Icomp2 which is added to the integral charge pump pulse Iint. This pulse Icomp2 only applies when the stobe line is high (loading either WORDA or WORDA2). When the strobe line is low there will be no Iint or Icomp2 pulses. The value of Icomp2 is given by

Icomp2 = Icomp(1).K

where K is a four bit number entered as part of the serial programming data.

Fig.6

Page 7

NJ88C50

MULTIMODULUS DIVISION

The NJ88C50 supports the use of 2, 3 and 4 modulus prescalers. Two modulus prescalers such as the SP8714/15 are commonly used in PLLs. Additional information on using 2 modulus prescalers can be found in application note AN132 in the GEC Plessey Semiconductors Personal Communications handbook (May 1992).

When using a 2 modulus prescaler (R/R+1) the minimum division ratio above which all channels can be synthesised is given by

Minimum division ratio = R(R-1)

eg. for a 64/65 prescaler such as the SP8714/15

Minimum division ratio = 64(64-1) = 4032

When fractional-N operation is being used higher comparison frequencies are used, which are obtained by using lower division ratios. Use of a 3 or 4 modulus prescaler allows the minimum division ratio to be lowered.

For a 3 modulus prescaler (R/R+1/R+A)

Minimum division ratio = R(R+A+1)+A

eg. for a 64/65/72 prescaler such as the SP8713

If a 64/65/72 prescaler is used all the channels will now be selectable as the minimum required division ratio will now be greater than the minimum allowable division ratio (1096).

SERIAL DATA BUS

The data needed to program the synthesiser is entered via a high speed (10MBit/s) 3-wire bus, with serial data, serial clock and strobe pins. The input data is partitioned so that after initial programming the output frequency can be changed by re-programming only 24 or 32 bits.The timing diagram for the bus is given in Fig.7.

The data is programmed as either four twenty-four bit words or three twenty-four bit words and one thirty-two bit word. When initially programmed words A, B, C and D are loaded, though if the auxiliary synthesiser is disabled C is not needed. Following the initial programming the frequency can be subsequently shifted in one of the following ways:

a) If a 2 or 3 ratio prescaler is being used and CN does

not need to be reprogrammed word A should be loaded.

b If a 2 or 3 ratio prescaler is being used and CN does

need to be reprogrammed word A2 should be loaded. In wide frequency band systems CN must be reprogrammed for best performance every time the frequency is changed.

c) If a four ratio prescaler is being used word A and word

B should be loaded

Minimum division ratio = 64(64+8+1)+8 = 1096

8 For a 4 modulus prescaler (R/R+1/R+A/R+B)

Minimum division ratio = R(A+B+R+1)+A+B

A B eg. for a 64/65/68/80 prescaler

Minimum division ratio = 64(4+16+64+1)+4+16 = 852

4 16

An example of where three modulus division would be implemented is given below.

The system in which the synthesiser is to operate has a lowest carrier frequency of 900MHz and a channel spacing of 30kHz. However due to the lock up time requirements fractional-N operation is being used in its 8ths mode (see section on fractional-N operation), giving a comparison frequency of 30kHz x 8 = 240kHz.

Therefore,

Minimum division ratio required = 900x106 = 3750

240x10

Data must be valid on positive edges of clock

Fig.7

A strobe pulse occurs at the end of each word and loads the contents of the input shift register into the working registers, except when word B is being loaded, in which case the shift register contents are loaded into a temporary register and then loaded into the working register when either word A or A2 is loaded. The information is transferred on the rising edge of the strobe pulse which should occur one half clock period after the clock edge on which the MSB of a word is shifted in.

If word A or word A2 is being loaded, when the strobe goes high the main synthesiser will be put into speed-up mode. This mode will be maintained while the strobe remains high. During this time any pulses on the clock input will not affect the function of the synthesiser.

If a 64/65 prescaler is used not all the channels will be selectable as the minimum required division ratio is less than the minimum allowable division ratio (4032).

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NJ88C50

The information contained within each word is given below. Data bits are shifted in on the leading clock edge, with the least significant bit(LSB) of the word first and the MSB of the word last. (Note that individual sections of data within a word are loaded with the MSB of that section first. An example of this is given after this description of Word A)

Word Format

MSB...........................................LSB

NF = Fractional-N incremental value. (MSB first) N1 = Number of cycles prescaler ratio R1 is used. (MSB first) N2 = Number of cycles prescaler ratio R2 is used. (MSB first) N3 = Number of cycles prescaler ratio R3 is used. (MSB first) If a two modulus prescaler is being used N2= 8 bits. If a three or four modulus prescaler is being used N2 = 4 bits and N2+N3= 4 bits(modulo-16 addition).

Therefore if the following values are required NF=3

N1=51 N2=25 the input word would be

0 110 110011000000 10011000

NF N1 N2

CN = Scaling factor for current setting. (MSB first)

Word B |1000 |N2+N3+N4| CN | K | L | P1,P2 |

N4 = Number of cycles prescaler ratio R4 is used and (N2+N3+N4) is modulo-16 addition. (MSB first) CN = Scaling factor for current setting. (MSB first) K = Acceleration factor for integral charge pump. (MSB first) L = Acceleration factor for proportional charge pump.

(MSB first)

P1,P2 = Number of modulii of prescaler.

Word D |1010 | NR |SM1,SM2| DM |SA1,SA2| DA|FMOD|LONG|

|12 bits| 2 bits | 1 bit | 2 bits |1 bit| 1 bit | 1 bit | NR = Reference frequency division value. (MSB first)

SM1,SM2 = Main reference source select (Rmain).

SM1 SM2 RMAIN 0 0 M 0 1 2M 1 0 4M 1 1 8M

SA1,SA2 = Auxiliary reference source select (Raux).

SA1 SA2 RAUX 0 0 M 0 1 2M 1 0 4M 1 1 8M

FMOD = Fractional-N modulus select (5 or 8).

FMOD MODULUS 0 5 1 8

DA = Disable auxiliary synthesiser.

DA=1-disabled DA=0-enabled

DM = Disable main synthesiser.

DM=1-disabled DM=0-enabled

LONG = Word A or A2 select.

LONG=0 Word A selected LONG=1 Word A2 selected

No. of modulii P2 P1

Two 0 0 Three 0 1

Four 1 0 Word C |1001| NA | |

| 12 bits | 8 bits free |

NA = Variable frequency for auxiliary synthesiser. (MSB first)

Page 9

ELECTRICAL CHARACTERISTICS

DC Characteristics

Vdd = 5V ± 10%, Tamb = -40 to +85°C

Static

NJ88C50

Parameter

Supply voltage Supply current

Min

4.5

DYNAMIC

AC Characteristics

Vdd = 5V ± 10%, Tamb = -40 to +85°C

Input signals - RF

Parameter

Input-RI

Reference input - Ri Rise time

Fall time Input voltage - Ri

Input capacitance Large signal input impedance Source impedance Z

Typ

5.0 6

3 4

2 4 2

Max

5.5

3 3

Min

0.1

0.25 200

Condition

Unit

Both synthesisers on

(Fia = 125MHz, Fim = 30MHz, Ri = 35MHz) Both synthesisers on

(Fia = 10MHz, Fim = 10MHz, Ri = 10MHz) Main on, Auxiliary in stand-by (Fim=30MHz, Ri=35MHz)

Main on, Auxiliary in stand-by (Fim=10MHz, Ri =10MHz)

Auxiliary on, Main in stand-by (Fia=125MHz, Ri=35MHz)

Auxiliary on, Main in stand-by (Fia=10MHz, Ri=10MHz)

Main and auxiliary in standby

µA

Typ

Max

35 35 20 20

1 1

1.5

Unit

MHz MHz

ns Vpk-pk Vpk-pk

kΩ kΩ

Condition

sinewave input, Note 1 pulse input, Note 1

Ri = 20-35MHz, Note 1 Ri = 10-19MHz, Note 1

Note 2 Note 3

Aux synthesiser input -FIA

Input frequency - Fia Rise time

Fall time Input voltage

Input capacitance Large signal input impedance Source impedance

Main synthesiser input -FIM

Input frequency - Fim Rise time

Fall time Input voltage Common mode input DC voltage range Input capacitance Input impedance Input Current

0.35

0.1

0.35 200

0.2

2.8

100

125 125

10 10

1 1 1

1.5

30 30 50 50

Vdd-1

10 10

MHz MHz

ns Vpk-pk Vpk-pk Vpk-pk

kΩ kΩ

MHz MHz

ns Vpk-pk

MΩ

µA

sinewave input, Note 1 pulse input, Note 1

Fia = 20-49MHz, Note 1 Fia = 50-99MHz, Note 1 Fia = 100-125MHz, Note 1

Note 2 Note 3

sinewave input pulse input

Single ended input

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NJ88C50

Notes

1. Source impedance = 50Ω

2. Virtual earth input amplifier, therfore low impedance for small signals. Impedance is high once signal amplitude exceeds typically ±0.125V.

3. Input amplifier may become unstable for higher values of ZS.

DYNAMIC

AC Characteristics

Vdd = 5V ± 10%, Tamb = -40 to +85°C

Input signals - Logic and current defining pins

Parameter

Data and strobe

Input voltage high Input voltage low Input capacitance Input current

Clock

Input voltage high Input voltage low Input capacitance Input current Input frequency

Current setting pins

Input Signal RSA Input current Input Signal RSM Input current Input Signal RSC Input current

Notes

1. The current set on pin RSA will be scaled up on chip by a factor of 3 to give the value of the auxiliary phase detector output.

Min

Vdd-0.8

Typ

80 32

12.8

Max

Vdd

0.8 10 10

Vdd

0.8 10 10 10

Unit

V V

µA

V V

µA

MHz

µA µA µA

Condition

Notes 1, 4 Notes 2, 4 Notes 3, 4

2. The current set on pin RSM will be scaled down on chip by a factor of 32 to provide the current Ibo to the main phase detector which gives the outputs I

3. The current set on pin RSC will be scaled down on chip by a factor of 128 to provide the current Ico to the main phase detector which gives the outputs I

4. The voltage on each of the three current setting pins (RSA, RSM, RSC) is approximately 4V. Therefore to give a typical current of 32µA on RSM for example, a 125kΩ resistor connected between the pin and GND would be required.

prop

comp

and I

int

comp 2

Page 11

DYNAMIC

Vdd = 5V ± 10%, Tamb = -40 to +85°C

Output signals

NJ88C50

Parameter

Modulus control - MOD1 MOD2

Output voltage high Output voltage low

Modulus output truth table

MOD2

0 0 1 1

DYNAMIC

Vdd = 5V, Tamb = -40 to +85°C

Output signals - Auxiliary synthesiser

Parameter

Output signal - PDA

Up current - See Note 5 Down current - See Note 5 Tristate

Min

Vdd-0.4

MOD1

1 0 0 1

Min

-10%

Typ

pda

Max

Vdd

0.4

Prescaler modulus

Max

+10% +10%

Unit

R1 R2 R3 R4

Unit

µA µA nA

Condition

Push-Pull output V V

IOH = 0.5mA

IOL = 0.5mA

Condition

0<VPD<4.35V

0.65<VPD<5V

DYNAMIC

Vdd = 5V, Tamb = -40 to +85°C

Output signals - Main synthesiser, proportional output

Parameter

Output signal - PDP

Iprop(0) Up see notes 1, 3 & 4 Iprop(0) Down see notes 1, 3 & 4 Iprop(1) Up see notes 2&3 Iprop(1) Down see notes 2&3 Tristate

Notes

1. The typical value of IPROP(0) is set by the programmed value of CN and the current I RSM, where Ibo=I

2. The typical value of IPROP(1) is set by the value of IPROP(0) and the programmed value of L.

3. The current output IPROP is specified between 100µA and 1mA.

4. The output current is monotonic over the CN range 128-255. In standard operation CN is set at a value > 128.

5. Where I

depends on the value of current setting resistor on RSA pin (9). I

pda

rsm

/ 32. I

is typically 32µA.

rsm

Min

-10%

Typ

+Ibo.CN

-Ibo.CN

+Ibo.CN.2

-Ibo.CN.2

L+1

Max

+10% +10% +10% +10%

Unit

max = 250µA

pda

Condition

µA

0<VPD<4.55V, Strobe=0V

µA

0.45<VPD<5V, Strobe=0V

µA

0<VPD<4.55V, Strobe=5V

µA

0.45<VPD<5V, Strobe=5V

set by the external resistor

rsm

Page 12

NJ88C50

DYNAMIC

Vdd = 5V, Tamb = -40 to +85°C

Output signals - Main synthesiser, integral output

Parameter

Min

Typ

Max

Unit

Output signal - PDI

IINT Up

-10%

+Ibo.CN.2

L+1

+10%

(1mA - 5mA) see notes 1&2

IINT Down

-10%

-Ibo.CN.2

L+1

+10%

(1mA - 5mA) see notes 1&2

IINT Up

-10%

+Ibo.CN.2

L+1

+10%

(5mA - 10mA) see notes 1&2

IINT Down

-10%

-Ibo.CN.2

L+1

+10%

(5mA - 10mA) see notes 1&2 Tristate

Notes

1. The typical value of IINT is set by the value of Iprop(1) and the programmed value of K.

2. The current output IINT is specified between 1mA and 10mA.

DYNAMIC

Vdd = 5V, Tamb = -40 to +85°C

Output signals - Main synthesiser, under Fractional-N control

Condition

0<VPD<4.45V, Strobe=5V

0.35<VPD<5V, Strobe=5V

0<VPD<4.3V, Strobe=5V

0.5<VPD<5V, Strobe=5V

Parameter

Min

Typ

Max

Unit

Condition

Output signal - PDP

ICOMP(0)

-10%

Ico.Acc.

+10%

µA

0<VPD<4.55V, Strobe=0V

see notes 1&3

ICOMP (1)

-10%

Ico.Acc.2

L+1

+10%

µA

0<VPD<4.55V, Strobe=5V

see notes 2&3

Output signal - PDI

ICOMP2

-10%

Ico.Acc.2

L+1

+10%

µA

0<VPD<4.55V, Strobe=5V

see notes 4&5

Notes

1. The typical value of ICOMP(0) is set by the fractional-N accumulator value Acc and the current I resistor RSC, where Ico=I

rsc

/128. I

is typically 12.8µA.

rsc

2. The typical value of ICOMP(1) is set by the value of ICOMP(0) and the programmed value of L.

3. The current output ICOMP is specified up to 12µA.

4. The typical value of ICOMP2 is set by the value of ICOMP(1) and the programmed value of K.

5. The current output ICOMP2 is specified up to 180µA.

set by the external

rsc

Page 13

NJ88C50

Fig.8 shows a typical application, using the NJ88C50 to generate both VHF and UHF signals. External components are kept to a minimum, requiring only bias, loop filter and decoupling components. In many applications the UHF VCO is a pre-assembled and tested module to suit the end equipment use, whereas the VHF design is likely to be discrete. The circuit shown is suitable for operation up to 1.1GHz and uses

a low power prescaler, the SP8715, feeding the NJ88C50 in single ended mode. This requires a biasing network around the differential input of the NJ88C50 to be used (pins 2 and 3).

Power supply and ground rails must have adequate

decoupling otherwise overall performance may be impaired.

Page 14

Page 15

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