MICRF620TR datasheet(12/18 Pages) MICREL

12 / 18 page

Micrel, Inc.

MICRF620

December 2005

M9999-120205

-45.0

-35.0

-25.0

-15.0

-5.0

5.0

15.0

25.0

35.0

45.0

55.0

121620242832

[XCO_tune value]

Figure 5. XCO Tuning

The typical start up time for the crystal oscillator (default

XCO_tune=13) is ~750us. If more capacitance is added

(higher XCO_tune value), then the start-up time will be

longer.

To save current in the crystal oscillator start-up period, the

XCO is turned on before any other circuit block. When the

XCO has settled, rest of the circuit will be turned on. No

programming should be made during this period.

The current consumption during the prestart period is

approximately 280µA.

VCO

A6..A0

0000011

‘1’

‘0’

VCO_IB2 VCO_IB1 VCO_IB0 VCO_freq1 VCO_freq0

The VCO has no external components. It has three bit to

set the bias current and two bit to set the VCO frequency.

These five bits are set by the RF frequency, as follows:

RF freq.

VCO_IB2

VCO_IB1

VCO_IB0

VCO_freq1 VCO_freq0

410MHz

434MHz

450MHz

Table 7. VCO Bit Setting

The bias bit will optimize the phase noise, and the

frequency bit will control a capacitor bank in the VCO. The

tuning range the RF frequency versus varactor voltage is

dependent on the VCO frequency setting, and can be

shown in Figure 6.

VCO frequency gain, Vdd=2.5V

380

400

420

440

460

480

0,4

0,8

1,2

1,6

2,4

V_varactor [V]

Figure 6. RF Frequency vs. Varactor Voltage

and VCO Frequency bit (VDD = 2.5V)

Lock Detect

A6..A0

0000001

‘1’

‘0’

RSSI_en

LD_en

PF_FC1

PF_FC0

A lock detector can be enabled by setting LD_en = 1.

When pin LD is high, it indicates that the PLL is in lock.

When entering TX, the procedure is first to load the TX

word and then turn on the PA stage. During the PA ramp

up time, the LD signal may indicate out of lock. It is first

when the PA stage is fully on that the LD signal will

indicate in “Lock”. During transmission, the Lock Detect

signal will have transitions and the user should therefore,

ignore the Lock detect signal.

Modes of Operation

A6..A0

0000000

LNA_by

PA2

PA1

PA0

Sync_en

Mode1

Mode0

’1’

Mode1

Mode0

State

Comments

Power down

Keeps register configuration

Standby

Only crystal oscillator running

Receive

Full receive

Transmit

Full transmit ex PA state

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