TLC2940

HIGH-PERFORMANCE CMOS VOLTAGE-CONTROLLED OSCILLATOR

SLAS244 – OCTOBER 1999

2

POST OFFICE BOX 655303

Terminal Functions

TERMINAL

I/O{

DESCRIPTION

NAME

NO.

I/O{

DESCRIPTION

BIAS

7

M

Bias supply terminal for internal VCO. The resistor should be located between VDD and this terminal.

FREFINPUT

3

I

Not used. This terminal should be tied to ground.

GND

5

PS

Ground

LOGIC VDD

1

PS

Power supply for the internal logic circuitry (PFD portion, input/output portion). It is recommended that this

terminal is separated from the VCO supply voltage terminal.

PFD OUT

4

O

Not used. This terminal should be unconnected (open).

VCOIN

6

I

VCO control voltage input.

VCO OUT

2

O

VCO output. This terminal is tied to a low level at inhibit status.

VCO VDD

8

PS

Supply voltage for VCO analog portion.

† I: Input, O: Output, PS: Power supply/GND, M: Others

detailed description

The TLC2940 is an analog VCO IC that generates a frequency that is a multiple of a reference frequency for

a PLL block configuration. Normally, a PLL block is composed of a VCO, a phase frequency detector, counter

logic, and a loop filter.

The following is a description for the analog VCO of the TLC2940.

The built-in analog VCO is composed of a ring oscillator portion for oscillation operation and a bias control

portion to generate a bias level to supply to the ring oscillator. The oscillation operation is performed by a bias

value increases, and the oscillation frequency increases as the resistor value decreases. The lock frequency

temperature range.

values.

VCO Oscillation Frequency Range

Bias Resistor (RBIAS)

VCO Control Voltage (VCOIN)

VCO Oscillation

Figure 1. VCO Oscillation Frequency Range Setting