TUA6032 Infineon Technologies Corporation, TUA6032 Datasheet - Page 20

• Manufacturer Part Number: TUA6032
• Description: 3-band Tv Tuner Ic
• Manufacturer: Infineon Technologies Corporation

Wireless Components
3.4.1
3.4.2
3.4 Circuit Description
Mixer-Oscillator block
The mixer-oscillator block includes three balanced mixers (one mixer with an
unbalanced high-impedance input and two mixers with a balanced low-imped-
ance input), two 2-pin asymmetrical oscillators for the LOW and the MID band,
one 4-pin symmetrical oscillator for the HIGH band, an IF amplifier, a reference
voltage, and a band switch.
Filters between tuner input and IC separate the TV frequency signals into three
bands. The band switching in the tuner front-end is done by using three PNP
port outputs. In the selected band the signal passes a tuner input stage with a
MOSFET amplifier, a double-tuned bandpass filter and is then fed to the mixer
input of the IC which has in case of LOW band a high-impedance input and in
case of MID or HIGH band a low-impedance input. The input signal is mixed
there with the signal from the activated on chip oscillator to the IF frequency
which is filtered out at the balanced mixer output pair by means of a parallel
tuned circuit. The following IF amplifier is capacitively coupled to the mixer out-
puts and has a low output impedance to drive the SAW filter directly.
PLL block
The oscillator signal is internally DC-coupled as a differential signal to the pro-
grammable divider inputs. The signal subsequently passes through a program-
mable divider with ratio N = 256 through 32767 and is then compared in a digital
frequency/phase detector with a reference frequency f
166.7 kHz. This frequency is derived from an unbalanced, low-impedance 4
MHz crystal oscillator (pin XTAL) divided by 128, 80,64 or 24. The reference fre-
quencies will be different with a quartz other than 4 MHz.
The phase detector has two outputs which drive two current sources of a charge
pump. If the negative edge of the divided VCO signal appears prior to the neg-
ative edge of the reference signal, the positive current source pulses for the
duration of the phase difference. In the reverse case the negative current
source pulses. If the two signals are in phase, the charge pump output (CP)
goes into the high-impedance state (PLL is locked). An active low-pass filter
integrates the current pulses to generate the tuning voltage for the VCO (inter-
nal amplifier, external pull-up resistor at VT and external RC circuitry). The
charge pump output is also switched into the high-impedance state if the control
bits T2, T1,T0 = 0, 1, 0. Here it should be noted, however, that the tuning volt-
age can alter over a long period in the high impedance state as a result of self
discharge in the peripheral circuity. VT may be switched off by the control bit OS
to allow external adjustments.
If the VCO is not oscillating the PLL locks to a tuning voltage of 33V (V
3 - 20
TUA6030, TUA6032
Functional Description
ref
= 31.25, 50, 62.5 or
Specification, July 2001
TH
).