TUA6036-T Infineon Technologies Corporation, TUA6036-T Datasheet - Page 24

• Manufacturer Part Number: TUA6036-T
• Description: 3-band Digital TV / Set-top-box Tuner IC
• Manufacturer: Infineon Technologies Corporation

2.4
2.4.1
The mixer-oscillator block includes three balanced mixers (one mixer with an
unbalanced high-impedance input and two mixers with a balanced low-impedance
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. The IF is filtered by means of an IF filter in between the 2 mixer
output pins and the 2 input pins of the following IF amplifier. The IF amplifier has a low
output impedance to drive the SAW filter directly.
2.4.2
The oscillator signal is internally DC-coupled as a differential signal to the programmable
divider inputs. The signal subsequently passes through a programmable divider with
ratio N = 256 through 32767 and is then compared in a digital frequency/phase detector
with a reference frequency f
frequency is derived from a balanced, low-impedance 4 MHz crystal oscillator (pins
XTAL, XTAL) divided by 128, 80, 64, 32, 28 or 24. The reference frequencies will be
different with a quartz other than 4 MHz.
The phase detector has two outputs which drive four current sources of a charge pump.
If the negative edge of the divided VCO signal appears prior to the negative 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 (internal 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 voltage
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.
Specification
Circuit Description
Mixer-Oscillator block
PLL block
ref
= 31.25, 50, 62.5, 125, 142.86 or 166.67 kHz. This
24
Functional Description
TUA6034, TUA6036
V 2.5, 2004-04-28