TUA6020 Infineon Technologies Corporation, TUA6020 Datasheet - Page 16

• Manufacturer Part Number: TUA6020
• Description: 2 Band Tv Tuner Mixer-oscillator-pll With Balanced If-amplifier
• Manufacturer: Infineon Technologies Corporation

Wireless Components
3.4.1
3.4.2
3.4 Circuit Description
Mixer-Oscillator block
The mixer oscillator section includes two balanced mixers (double balanced
mixer), two balanced oscillators for LOW/MID and HIGH, an IF amplifier, a ref-
erence voltage source and a band switch.
Filters between tuner input and IC separate the TV frequency signals into two
bands. The band switching in the tuner front-end is done by using two or three
port outputs. In the selected band the signal passes a tuner input stage with
MOSFET amplifier, a double-tuned bandpass filter and is then fed to the bal-
anced mixer input of the IC which has in case of LOW / MID a high-impedance
input and in case of HIGH 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 high-impedance output pair by means of a
parallel tuned circuit. The following SAW preamplifier has a low output imped-
ance 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 to a reference frequency f
166.7 kHz.This frequency is derived from an unbalanced, low-impedance 4
MHz crystal oscillator (pin XTAL) divided by R = 128, 80, 64 or 24.
The phase detector has two outputs that drive two current sources of opposite
polarity as 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 I- 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 TUNE and external RC circuitry). The
charge pump output is also switched into the high-impedance state if the control
bits T0 = 1 and T1 = 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-dis-
charge in the peripheral circuitry. TUNE 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
By means of control bit CP the pump current can be switched between two val-
ues by software. This programmability permits alteration of the control response
time of the PLL in the locked-in state. In this way different VCO gains can be
compensated, for example.
3 - 8
ref
Functional Description
= 31.25, 50, 62.5 or
Specification, April 2000
preliminarytarget
TUA6020
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