HD155111F Datasheet, PDF (9/44 Pages) Hitachi Semiconductor – RF Single-chip Linear IC for PCN Cellular Systems

HD155111F
Functional Operation
The HD155111F has been designed from system stand point and incorporated a large number of the circuit
blocks necessary in the design of a digital cellular handset.
Receiver Operation
The HD155111F incorporates a LNA bias circuit for an external RF transistor, whose NF and power gain
can be better selected.
This circuit amplifies the RF signal after selection by the antenna filter before the signal enters the first
mixer section. The RF signal is combined with a low side local oscillator (LO) signal to generate a wanted
first IF signal in the 130 to 300 MHz range. The 1st mixer circuit uses a double-balanced Gilbert cell
architecture, which has open collector differential outputs. If, at 225 MHz, a 800 Ω LC load is connected
to the mixer’s outputs then a SSB NF of 10 dB with a gain of 8.0 dB is realizable. The corresponding input
compression point is –13 dBm, which allows the device to be used within a PCN system.
A filter is used after the 1st mixer to provide image rejection and the conditioned signal is then passed
through an intermediate amplifier, before being down converted to a second IF in the range of 26 to 60
MHz.
The second mixer can generate a 45 MHz 2nd IF, if a 270 MHz 2nd LO signal is used. The 2nd LO is
obtained by dividing the IFLO signal by 2. The 2nd mixer also uses the Gilbert cell architecture, but with
internal resistive differential outputs of 300 Ω. IF amplifier and second mixer has a SSB NF of 5.6 dB, a
power gain of 12 dB and an input compression point of –25 dBm. In order to improve the blocking
characteristics of the device an external LC resonator across the differential outputs of the second mixer is
recommended.
The signal is then passed to the AGC circuit, which has a dynamic range of more than 80 dB (–42 dB to
+55 dB Typ) and is controlled by a DC voltage, which is generated by the microprocessor. This DC
control range is from 0.15 V to 2.3 V. The AGC, which is designed for the PCN system, provides a
linearity of ±1.0 dB in any 20 dB window. The outputs of the AGC are 2 kΩ differential and are connected
the external supply via inductors.
The signal is then down converted by a demodulator to I and Q. Internal divider circuits convert the IFLO
signal to the same frequency as the 2nd IF before passing this local signal through a phase splitter / shifter
in order to generate the in phase and quadrature IQ components. The phase accuracy of the IQ
demodulator is < ±1° and the amplitude mismatch is < ±0.5 dB. In order to accommodate different
baseband interfaces the HD155111F IQ differential outputs have a voltage swing of 2.4 Vp-p and a DC
offset of < 60 mV Max. Within each output stage a 2nd order Butterworth filter (fc = 210 kHz), is used to
improve the blocking performance of the device.
In order to allow flexibility in circuit implementation the HD155111F can configured to use either a single-
ended or balanced external circuitry and components.