MICRF507 datasheet(24/47 Pages) MICREL

24 / 47 page

Micrel, Inc.

MICRF507

October 2, 2013

Revision 2.2

Receiver

Field Name

Number

of bits

Location

of bits

Description

Reference

By_LNA

Reg0[7]

LNA bypass on/off

PF_FC

Reg1[1:0]

Pre-filter corner frequency

Table 14

SC_by

Reg2[6]

Bypass of switched capacitor filter on/off

ScClk

Reg8[4:0]

Switched Cap clock divider

RSSI_en

Reg1[3]

RSSI function on/off

FEEC

Reg21[3:0]

FEE control bits

Table 15

FEE

Reg22[7:0]

FEE value (read only)

Table 13. Register Bit Fields for Receiver

The receiver is a zero intermediate frequency (ZIF) type

employing low-power, fully integrated low-pass filters.

A low noise amplifier (LNA) drives a quadrature mixer pair.

The mixer outputs feed two identical signal channels.

Each channel’s signal path has a pre-amplifier, a third

order

Sallen-Key RC

low-pass

pre-filter,

six-pole

switched-capacitor

filter

(which

determines

actual

selectivity), and finally a limiter.

The limiter outputs then enter a demodulator which detects

the relative phase of the baseband I and Q signals. If the I

channel signal lags the Q channel, the FSK tone frequency

lies above the LO frequency (data ‘1’). If the I channel

leads the Q channel, then the FSK tone lies below the LO

frequency (data ‘0’). The output of the demodulator is

available on the DATAIXO pin; in either raw form or

latched with the recovered clock according to the setting of

Sync_en bit. An RSSI (receive signal strength indicator)

circuit indicates the received signal level.

Front End

The MICRF507’s low-noise amplifier boosts the incoming

signal prior to frequency conversion in order to prevent

mixer noise from

degrading overall front-end noise

performance. The LNA is a two-stage amplifier and has a

nominal gain of approximately 23dB at 490MHz. The front

end has a gain of about 31dB to34dB. The gain varies by

1-1.5dB over a 2.0V to 2.5V variation in power supply.

The LNA can be bypassed by setting bit LNA_by to ‘1’.

This can be useful for very strong input signal levels. The

front-end gain with the LNA bypassed is about 12dB. The

mixers have about 10dB of gain at 490MHz. With

appropriate setting of the OUTS field (register 2, bits D3 to

D0), the differential outputs of the mixers can be made

available

pins

IchOut

and

QchOut.

The

output

impedance of each mixer is about 8k

Ω.

Figure 15. LNA Input Impedance

RESISTANCE

32.4

Ω

33.4

Ω

34.4

Ω

REACTANCE

7.9

Ω

7.4

Ω

6.4

Ω

MHz

470

490

510

MARKER

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