th71112 Melexis Company, th71112 Datasheet - Page 4

• Manufacturer Part Number: th71112
• Description: Receiver - 868/915mhz Fsk/ask, Double-conversion Superhet Lqfp32
• Manufacturer: Melexis Company

1.3
1.4
Note: ENRX are pulled down internally
1.5
Note: hysteresis between gain modes to ensure stability
1.6
Frequency planning is straightforward for single-conversion applications because there is only one IF that
can be chosen, and then the only possible choice is low-side or high-side injection of the LO signal (which is
now the one and only LO signal in the receiver).
The receiver’s double-conversion architecture requires careful frequency planning. Besides the desired RF
input signal, there are a number of spurious signals that may cause an undesired response at the output.
Among them are the image of the RF signal (that must be suppressed by the RF front-end filter), spurious
signals injected to the first IF (IF1) and their images which could be mixed down to the same second IF (IF2)
as the desired RF signal (they must be suppressed by the LC filter at IF1 and/or by low-crosstalk design).
39010 71112
Rev. 014
Block Diagram
Mode Configurations
LNA GAIN Control
Frequency Planning
V
< 0.8 V
> 1.4 V
IN_LNA
31
ENRX
GAIN_LNA
32
1
0
1
LNA
30
2
3
4
VCO1
DIV16
MIX1
5
LO1
HIGH GAIN
RX standby
LOW GAIN
RX active
29
6
Mode
Mode
LF
DIV2
IF1
Fig. 1: TH71112 block diagram
7
CP
MIX2
8
PFD
LO2
9
Page 4 of 22
IF2
10
26
RO
RO
11
12
25
13
27
IFA
21
28
LNA set to high gain
LNA set to low gain
BIAS
14
Description
Description
RX disabled
RX enable
15
22
FSK/ASK Receiver
MIX3
16
17
TH71112
868/915MHz
OA
OUT_OA
OUTN
OUTP
OAN
OAP
Data Sheet
23
24
20
19
18
April/08