ML2712CH データシートの表示（PDF） - Micro Linear Corporation

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ML2712CH

2.4GHz RF Transceiver

Micro Linear Corporation 

PRELIMINARY

ML2712

MODES OF OPERATION

STANDBY MODE

Tx VCO

In STANDBY mode all the PLL and VCO circuits are

Tuning

Voltage

enabled while all the transmitter and receiver circuits

are disabled. (see Figigure 1) The use of STANDBY

mode is recommended when the PLLs are locking, after

the PLL frequencies have been reprogrammed, or after the

IC has been transferred out of SLEEP mode. The VCO and

PLL circuits are enabled and reach a locked state in 150

usec indicated by an active Lock Detect (LD) signal.The

frequency divide ratio settings defined by Control Word C

Rx RF

and D (see Table 4 ) define the frequencies of the 1LO

Input

PLL and 2LO PLL.

TRANSMIT MODE

Rx RF

Input

The ML2712 uses a directly modulated VCO running

at the transmitter frequency to generate the

transmited signal. The VCO is then free of unwanted

spurious signals and has the advantage of requiring

no bandpass filtering for the transmitter signal prior

to or after the Power Amplifier. The transmitter VCO

is phase locked to the center frequency with the

transmitter modulation applied. The modulated signal

is applied directly to the VCO inside the loop

bandwidth of a phase locked loop. To allow

Tx VCO

Tuning

modulation rates in excess of 1Mbps requires a very Voltage

wideband phase detector, capable of operating with

loop bandwidths in excess of 5MHz. In this circuit

the noise floor is set by the transmit VCO rather than

by upconvert mixers. The circuits active in TRANSMIT

Mode are shown in Figure 2.

DIRECTLY MODULATED TRANSMIT VCO

The transmitter is designed to enable a significant amount Tx RF

of power to be generated at the required frequency using Input

a VCO, and is a technique for generating low noise,

phase/frequency modulated transmitters without the need

for bandpass filtering.

Rx RF

Input

The ML2712 transmitter architecture is shown Figure 3. A

tuning voltage applied to the transmit VCO, operating at

the final transmission frequency, ensures the correct

center frequency before modulation is applied. This closed

loop system, uses a PLL with the Transmit VCO phase

locked to a modulated reference signal (SMOD). The

modulated reference signal is generated at 260MHz. The

signal from the Transmit VCO is down converted with the

1LO signal, then filtered through a bandpass filter. The

output of the filter is fed to the very high-speed phase/

frequency detector Wideband PLL. This compares the

down-converted transmit signal with the modulated

reference signal SMOD.

Any frequency or phase error between SMOD and the

down-converted signal is corrected by changing the

tuning voltage of the transmit VCO. The down-conversion

with the F1LO translates the reference signal SMOD to the

final transmitter frequency.

Control

Interface

RSSI

WB

Charge

Pump

WB

Phase

Comp

LPF

Active

Control

+

DAC

–

2LO VCO

PLL 2

Lock

Detect

x2

MUX

PLL 1

1LO VCO

Disabled

ML2712

RSSI A/D

Comparator

Output

2LO Output

To IF Transceiver

2LO Loop

Filter &

Tank Circuit

Lock Detect

Ref Frequency Input

1LO Loop

Filter &

Tank Circuit

1IF Input

Output

Figure 1. Standby Mode Active Circuits

Control

Interface

RSSI

WB

Charge

Pump

WB

Phase

Comp

LPF

Control

x2

MUX

+

DAC

–

2LO VCO

PLL 2

Lock

Detect

PLL 1

1LO VCO

ML2712

RSSI A/D

Comparator

Output

2LO Output

To IF Transceiver

2LO Loop

Filter &

Tank Circuit

Lock Detect

Ref Frequency Input

1LO Loop

Filter &

Tank Circuit

1IF Input/

Output

Active

Disabled

Figure 2. Transmit Mode Active Circuits

TRANSMIT SIGNAL

(SMOD + F1LO)

ERROR

CORRECTION

LOOP

FILTER

RF DOWN

CONVERTER

SMOD +

PLL

ERROR SIGNAL

SMOD

LOW PASS

FILTER

FREQUENCY = F1LO

SMOD = CARRIER FREQUENCY

+ MODULATION

Figure 3. Directly Modulated VCO Transmitter

8

PRELIMINARY DATASHEET January, 2000

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