MICRF620TR datasheet(11/18 Pages) MICREL

11 / 18 page

Micrel, Inc.

MICRF620

December 2005

M9999-120205

Programming Summary

•

Use CS, SCLK, and IO to get access to the control

registers in MICRF620.

•

SCLK is user-controlled.

•

Write to the MICRF620 at positive edges

(MICRF620 reads at negative edges).

•

Read from the MICRF620 at negative edges

(MICRF620 writes at positive edges)

•

After power-on: Write to the complete set of

control registers.

•

Address field is 7 bits long. Enter msb first.

•

R/W bit is 1 bit long (“1” for read, “0” for write)

•

Address and R/W bit together make 1 octet

•

All control registers are 8 bits long. Enter/read msb

in every octet first.

•

Always write 8 bits to/read 8 bits from a control

than 8 used programming bits as well.

•

Writing: Bring CS high, write address and R/W bit

followed by the new values to fill into the

addressed control register(s) and bring CS low for

loading, i.e., activation of the new control register

values.

•

Reading: Bring CS high, write address and R/W

bit, set IO as an input, read present contents of the

addressed control register(s), bring CS low and

set IO an output.

Frequency Synthesizer

A6…A0

0001010

A0_5

A0_4

A0_3

A0_2

A0_1

A0_0

0001011

N0_11

N0_10

N0_9

N0_8

0001100

N0_7

N0_6

N0_5

N0_4

N0_3

N0_2

N0_1

N0_0

0001101

M0_11

M0_10

M0_9

M0_8

0001110

M0_7

M0_6

M0_5

M0_4

M0_3

M0_2

M0_1

M0_0

0001111

A1_5

A1_4

A1_3

A1_2

A1_1

A1_0

0010000

N1_11

N1_10

N1_9

N1_8

0010001

N1_7

N1_6

N1_5

N1_4

N1_3

N1_2

N1_1

N1_0

0010010

M1_11

M1_10

M1_9

M1_8

0010011

M1_7

M1_6

M1_5

M1_4

M1_3

M1_2

M1_1

M1_0

The frequency synthesizer consists of a voltage-controlled

oscillator (VCO), a crystal oscillator, phase select

prescaler, programmable frequency dividers and a phase-

detector. The length of the N, M, and A registers are 12,

12 and 6 respectively. The N, M, and A values can be

calculated from the formula:

() ()

VCO

XCO

PhD

≤ A < N

PhD: Phase detector comparison frequency

fXCO: Crystal oscillator frequency

fVCO: Voltage controlled oscillator frequency

fRF: Input/output RF frequency

There are two sets of each of the divide factors (i.e. A0

and A1). Storing the ‘0’ and the ‘1’ frequency in the 0- and

the 1 registers respectively, does the 2-FSK. The receive

frequency must be stored in the ‘0’ registers.

Crystal Oscillator (XCO)

Adr

0001001

‘0’

‘1’

XCOtune4

XCOtune3

XCOtune2

XCOtune1

XCOtune0

The crystal oscillator is a reference for the RF output

frequency and the LO frequency in the receiver. It is

possible to tune the internal crystal oscillator by switching

in internal capacitance using 5 tune bits XCOtune4 –

XCOtun0. The benefit of tuning the crystal oscillator is to

eliminate the initial tolerance and the tolerance over

temperature and aging. By using the crystal tuning feature

the noise bandwidth of the receiver can be reduced and a

higher sensitivity is achieved.

When XCOtune4 –

XCOtune0 = 0 no internal capacitors are connected to the

crystal pins. When XCOtune4 – XCOtune0 = 1 all of the

internal capacitors are connected to the crystal pins.

Figure 5 shows the tuning range.

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