TDA5204E1 Datasheet, PDF (18/40 Pages) Infineon Technologies AG – ASK Single Conversion Receiver 390MHz

TDA 5204 E1
preliminary
Functional Description
3.4.5 Limiter
The Limiter is an AC coupled multistage amplifier with a cumulative gain of
approximately 80dB that has a bandpass-characteristic centred around
10.7MHz. It has an input impedance of 330 Ω=to allow for easy interfacing to a
10.7MHz ceramic IF filter. The limiter circuit acts as a Receive Signal Strength
Indicator (RSSI) generator which produces a DC voltage that is directly propor-
tional to the input signal level as can be seen in Figure 4.1. This signal is used
to demodulate the ASK receive signal in the subsequent baseband circuitry and
to turn down the LNA gain by approximately 18dB in case the input signal
strength is too strong as described in Section 3.4.1 and Section 4.1.
3.4.6 Data Filter
The data filter comprises an OP-Amp with a bandwidth of 100kHz used as a
voltage follower and two 100kΩ= on-chip resistors. Along with two external
capacitors a 2nd order Sallen-Key low pass filter is formed. The selection of the
capacitor values is described in Section 4.2.
3.4.7 Data Slicer
The data slicer is a fast comparator with a bandwidth of 100 kHz. This allows
for a maximum receive data rate of approximately 120kBaud. The maximum
achievable data rate also depends on the IF Filter bandwidth and the local oscil-
lator tolerance values. Both inputs are accessible. The output delivers a digital
data signal (CMOS-like levels) for the detector. The self-adjusting threshold on
pin SLN (pin 20) its generated by RC-term or peak detector depending on the
baseband coding scheme. The data slicer threshold generation alternatives are
described in more detail in Section 4.5.
3.4.8 Peak Detector
The peak detector generates a DC voltage which is proportional to the peak
value of the receive data signal. An external RC network is necessary. The out-
put can be used as an indicator for the signal strength and also as a reference
for the data slicer. The maximum output current is approx. 900µA.
Wireless Components
3 - 10
Specification, December 2000